Awesome

Rambdax

Extended version of Rambda(utility library) - Documentation

Rambda is smaller and faster alternative to the popular functional programming library Ramda. - Documentation

❯ Differences between Rambda and Rambdax

Rambdax passthrough all Rambda methods and introduce some new functions.

The idea of Rambdax is to extend Rambda without worring for Ramda compatibility.

❯ Example use

import { composeAsync, filter, delay, mapAsync } from 'rambdax'

const result = await composeAsync(
  mapAsync(async x => {
    await delay(100)
    return x + 1
  }),
  filter(x => x > 1)
)([1, 2, 3])
// => [3, 4]

You can test this example in <a href="https://rambda.now.sh?const%20result%20%3D%20await%20R.composeAsync(%0A%20%20R.mapAsync(async%20x%20%3D%3E%20%7B%0A%20%20%20%20await%20R.delay(100)%0A%20%20%20%20return%20x%20%2B%201%0A%20%20%7D)%2C%0A%20%20R.filter(x%20%3D%3E%20x%20%3E%201)%0A)(%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%5B3%2C%204%5D">Rambda's REPL</a>

• Differences between Rambda and Ramda
• API
• Changelog

❯ Rambdax's advantages

TypeScript included

TypeScript definitions are included in the library, in comparison to Ramda, where you need to additionally install @types/ramda.

Still, you need to be aware that functional programming features in TypeScript are in development, which means that using R.compose/R.pipe can be problematic.

Important - Rambdax version 9.0.0(or higher) requires TypeScript version 4.3.3(or higher).

Dot notation for R.path, R.paths, R.assocPath and R.lensPath

Standard usage of R.path is R.path(['a', 'b'], {a: {b: 1} }).

In Rambda you have the choice to use dot notation(which is arguably more readable):

R.path('a.b', {a: {b: 1} })

Comma notation for R.pick and R.omit

Similar to dot notation, but the separator is comma(,) instead of dot(.).

R.pick('a,b', {a: 1 , b: 2, c: 3} })
// No space allowed between properties

Extendable with Ramda community projects

Rambdax implements some methods from Ramda community projects, such as R.lensSatisfies, R.lensEq and R.viewOr.

Understandable source code due to little usage of internals

Ramda uses a lot of internals, which hides a lot of logic. Reading the full source code of a method can be challenging.

Better VSCode experience

If the project is written in Javascript, then go to source definition action will lead you to actual implementation of the method.

Deno support

import * as R from "https://deno.land/x/rambdax/mod.ts";

Alternative TS definitions

Alternative TS definitions are available as rambdax/immutable. These are Rambdax definitions linted with ESLint functional/prefer-readonly-type plugin.

❯ Missing Ramda methods

• construct - Using classes is not very functional programming oriented.
• constructN - same as above
• into - no support for transducer as it is overly complex to implement, understand and read.
• invert - overly complicated and limited use case
• invertObj
• invoker
• keysIn - we shouldn't encourage extending object with .prototype
• lift
• liftN
• mapAccum - Ramda example doesn't looks convincing
• mapAccumRight
• memoizeWith - hard to imagine its usage in context of R.pipe/R.compose
• mergeDeepWith - limited use case
• mergeDeepWithKey
• mergeWithKey
• nAry - hard to argument about and hard to create meaningful TypeScript definitions
• nthArg - limited use case
• o - enough TypeScript issues with R.pipe/R.compose to add more composition methods
• otherwise - naming is confusing
• pair - left-pad types of debacles happens partially because of such methods that should not be hidden, bur rather part of your code base even if they need to exist.
• partialRight - I dislike R.partial, so I don't want to add more methods that are based on it
• pipeWith
• project - naming is confusing, but also limited use case
• promap
• reduceRight - I find right/left methods confusing so I added them only where it makes sense.
• reduceWhile - functions with 4 inputs - I think that even 3 is too much
• reduced
• remove - nice name but it is too generic. Also, Rambdax has such method and there it works very differently
• scan - hard to explain
• sequence
• splitWhenever
• symmetricDifferenceWith
• andThen
• toPairsIn
• transduce - currently is out of focus
• traverse - same as above
• unary
• uncurryN
• unfold - similar to R.scan and I find that it doesn't help with readability
• unionWith - why it has its usage, I want to limit number of methods that accept more than 2 arguments
• until
• useWith - hard to explain
• valuesIn
• xprod - limited use case
• thunkify
• __ - placeholder method allows user to further customize the method call. While, it seems useful initially, the price is too high in terms of complexity for TypeScript definitions. If it is not easy exressable in TypeScript, it is not worth it as Rambda is a TypeScript first library.

The following methods are not going to be added(reason for exclusion is provided as a comment):

❯ Install

• yarn add rambdax

• For UMD usage either use ./dist/rambdax.umd.js or the following CDN link:

https://unpkg.com/rambdax@CURRENT_VERSION/dist/rambdax.umd.js

• with deno

import {add} from "https://deno.land/x/rambda/mod.ts";

Differences between Rambda and Ramda

• Rambda's type detects async functions and unresolved Promises. The returned values are 'Async' and 'Promise'.

• Rambda's type handles NaN input, in which case it returns NaN.

• Rambda's forEach can iterate over objects not only arrays.

• Rambda's map, filter, partition when they iterate over objects, they pass property and input object as predicate's argument.

• Rambda's filter returns empty array with bad input(null or undefined), while Ramda throws.

• Ramda's clamp work with strings, while Rambda's method work only with numbers.

• Ramda's indexOf/lastIndexOf work with strings and lists, while Rambda's method work only with lists as iterable input.

• Error handling, when wrong inputs are provided, may not be the same. This difference will be better documented once all brute force tests are completed.

• TypeScript definitions between rambda and @types/ramda may vary.

❯ Benchmarks

There are methods which are benchmarked only with Ramda and Rambda(i.e. no Lodash).

Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.

The benchmarks results are produced from latest versions of Rambda, Lodash(4.17.21) and Ramda(0.30.1).

❯ Used by

• ESLint plugin Mocha

• WatermelonDB

• Walmart Canada reported by w-b-dev

• VSCode Slack integration

• Webpack PostCSS

• MobX-State-Tree decorators

• Rewrite of the Betaflight configurator

• MineFlayer plugin

API

add

It adds a and b.

:boom: It doesn't work with strings, as the inputs are parsed to numbers before calculation.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.add(2%2C%203)%20%2F%2F%20%3D%3E%20%205">Try this <strong>R.add</strong> example in Rambda REPL</a>

addIndex

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.addIndex(R.map)((val%2C%20idx)%20%3D%3E%20val%20%2B%20idx%20%2B%201%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%5B2%2C%204%2C%206%5D">Try this <strong>R.addIndex</strong> example in Rambda REPL</a>

addIndexRight

Same as R.addIndex, but it will passed indexes are decreasing, instead of increasing.

adjust

adjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[]

It replaces index in array list with the result of replaceFn(list[i]).

const result = R.adjust(
  0,
  a => a + 1,
  [0, 100]
) // => [1, 100]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.adjust(%0A%20%200%2C%0A%20%20a%20%3D%3E%20a%20%2B%201%2C%0A%20%20%5B0%2C%20100%5D%0A)%20%2F%2F%20%3D%3E%20%5B1%2C%20100%5D">Try this <strong>R.adjust</strong> example in Rambda REPL</a>

import { cloneList } from './_internals/cloneList.js'
import { curry } from './curry.js'

function adjustFn(
  index, replaceFn, list
){
  const actualIndex = index < 0 ? list.length + index : index
  if (index >= list.length || actualIndex < 0) return list

  const clone = cloneList(list)
  clone[ actualIndex ] = replaceFn(clone[ actualIndex ])

  return clone
}

export const adjust = curry(adjustFn)

import { add } from './add.js'
import { adjust } from './adjust.js'
import { pipe } from './pipe.js'

const list = [ 0, 1, 2 ]
const expected = [ 0, 11, 2 ]

test('happy', () => {})

test('happy', () => {
  expect(adjust(
    1, add(10), list
  )).toEqual(expected)
})

test('with curring type 1 1 1', () => {
  expect(adjust(1)(add(10))(list)).toEqual(expected)
})

test('with curring type 1 2', () => {
  expect(adjust(1)(add(10), list)).toEqual(expected)
})

test('with curring type 2 1', () => {
  expect(adjust(1, add(10))(list)).toEqual(expected)
})

test('with negative index', () => {
  expect(adjust(
    -2, add(10), list
  )).toEqual(expected)
})

test('when index is out of bounds', () => {
  const list = [ 0, 1, 2, 3 ]
  expect(adjust(
    4, add(1), list
  )).toEqual(list)
  expect(adjust(
    -5, add(1), list
  )).toEqual(list)
})

all

all<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if all members of array list returns true, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > -1

const result = R.all(predicate, list)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%200%2C%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%20-1%0A%0Aconst%20result%20%3D%20R.all(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.all</strong> example in Rambda REPL</a>

export function all(predicate, list){
  if (arguments.length === 1) return _list => all(predicate, _list)

  for (let i = 0; i < list.length; i++){
    if (!predicate(list[ i ])) return false
  }

  return true
}

import { all } from './all.js'

const list = [ 0, 1, 2, 3, 4 ]

test('when true', () => {
  const fn = x => x > -1

  expect(all(fn)(list)).toBeTrue()
})

test('when false', () => {
  const fn = x => x > 2

  expect(all(fn, list)).toBeFalse()
})

allFalse

allFalse(...inputs: any[]): boolean

It returns true if all inputs arguments are falsy(empty objects and empty arrays are considered falsy).

Functions are valid inputs, but these functions cannot have their own arguments.

This method is very similar to R.anyFalse, R.anyTrue and R.allTrue

R.allFalse(0, null, [], {}, '', () => false)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.allFalse(0%2C%20null%2C%20%5B%5D%2C%20%7B%7D%2C%20''%2C%20()%20%3D%3E%20false)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.allFalse</strong> example in Rambda REPL</a>

import { isTruthy } from './_internals/isTruthy.js'
import { type } from './type.js'

export function allFalse(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isTruthy(x())){
        return false
      }
    } else if (isTruthy(x)){
      return false
    }

    counter++
  }

  return true
}

import { runTests } from 'helpers-fn'

import { allFalse } from './allFalse.js'

const happy = { ok : [ () => false, () => [], () => {}, null, false, [] ] }
const withArray = { fail : [ ...happy.ok, [ 1 ] ] }
const withObject = { fail : [ ...happy.ok, { a : 1 } ] }
const withFunction = { fail : [ ...happy.ok, () => ({ a : 1 }) ] }
const withBoolean = { fail : [ ...happy.ok, true ] }

const testData = {
  label : 'R.allFalse',
  data  : [ happy, withArray, withObject, withFunction, withBoolean ],
  fn    : input => allFalse(...input),
}
runTests(testData)

allPass

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It returns true, if all functions of predicates return true, when input is their argument.

const input = {
  a : 1,
  b : 2,
}
const predicates = [
  x => x.a === 1,
  x => x.b === 2,
]
const result = R.allPass(predicates)(input) // => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20input%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%202%2C%0A%7D%0Aconst%20predicates%20%3D%20%5B%0A%20%20x%20%3D%3E%20x.a%20%3D%3D%3D%201%2C%0A%20%20x%20%3D%3E%20x.b%20%3D%3D%3D%202%2C%0A%5D%0Aconst%20result%20%3D%20R.allPass(predicates)(input)%20%2F%2F%20%3D%3E%20true">Try this <strong>R.allPass</strong> example in Rambda REPL</a>

export function allPass(predicates){
  return (...input) => {
    let counter = 0
    while (counter < predicates.length){
      if (!predicates[ counter ](...input)){
        return false
      }
      counter++
    }

    return true
  }
}

import { allPass } from './allPass.js'

test('happy', () => {
  const rules = [ x => typeof x === 'number', x => x > 10, x => x * 7 < 100 ]

  expect(allPass(rules)(11)).toBeTrue()

  expect(allPass(rules)(undefined)).toBeFalse()
})

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 2 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeTrue()
})

test('when returns false', () => {
  const conditionArr = [ val => val.a === 1, val => val.b === 3 ]

  expect(allPass(conditionArr)({
    a : 1,
    b : 2,
  })).toBeFalse()
})

test('works with multiple inputs', () => {
  const fn = function (
    w, x, y, z
  ){
    return w + x === y + z
  }
  expect(allPass([ fn ])(
    3, 3, 3, 3
  )).toBeTrue()
})

allTrue

allTrue(...input: any[]): boolean

It returns true if all inputs arguments are truthy(empty objects and empty arrays are considered falsy).

R.allTrue(1, true, {a: 1}, [1], 'foo', () => true)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.allTrue(1%2C%20true%2C%20%7Ba%3A%201%7D%2C%20%5B1%5D%2C%20'foo'%2C%20()%20%3D%3E%20true)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.allTrue</strong> example in Rambda REPL</a>

import { isFalsy } from './_internals/isFalsy.js'
import { type } from './type.js'

export function allTrue(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isFalsy(x())){
        return false
      }
    } else if (isFalsy(x)){
      return false
    }

    counter++
  }

  return true
}

import { allTrue } from './allTrue.js'

test('with functions', () => {
  const foo = () => 1
  const bar = () => false
  const baz = () => JSON.parse('{sda')
  const result = allTrue(
    foo, bar, baz
  )
  expect(result).toBeFalse()
})

test('usage with non boolean', () => {
  const foo = { a : 1 }
  const baz = [ 1, 2, 3 ]

  const result = allTrue(
    foo, foo, baz
  )
  expect(result).toBeTrue()
})

test('usage with boolean', () => {
  const foo = 4
  const baz = [ 1, 2, 3 ]

  const result = allTrue(foo > 2, baz.length === 3)
  expect(result).toBeTrue()
})

test('escapes early - case 0', () => {
  const foo = undefined
  const result = allTrue(foo, () => foo.a)
  expect(result).toBeFalse()
})

test('escapes early - case 1', () => {
  const foo = null
  const result = allTrue(foo, () => foo.a)
  expect(result).toBeFalse()
})

test('escapes early - case 2', () => {
  const foo = { a : 'bar' }
  const result = allTrue(
    foo, foo.a, foo.a.b
  )
  expect(result).toBeFalse()
})

test('escapes early - case 3', () => {
  const foo = { a : { b : 'foo' } }
  const result = allTrue(
    foo,
    () => foo.a,
    () => foo.a.b
  )
  expect(result).toBeTrue()
})

allType

allType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if all of its inputs arguments belong to targetType.

:boom: targetType is one of the possible returns of R.type

const targetType = 'String'

const result = R.allType(
  targetType
)('foo', 'bar', 'baz')
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20targetType%20%3D%20'String'%0A%0Aconst%20result%20%3D%20R.allType(%0A%20%20targetType%0A)('foo'%2C%20'bar'%2C%20'baz')%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.allType</strong> example in Rambda REPL</a>

import { type } from './type.js'

export function allType(targetType){
  return (...inputs) => {
    let counter = 0

    while (counter < inputs.length){
      if (type(inputs[ counter ]) !== targetType){
        return false
      }
      counter++
    }

    return true
  }
}

import { allType } from './allType.js'

test('when true', () => {
  const result = allType('Array')(
    [ 1, 2, 3 ], [], [ null ]
  )

  expect(result).toBeTrue()
})

test('when false', () => {
  const result = allType('String')(
    1, undefined, null, []
  )

  expect(result).toBeFalse()
})

always

It returns function that always returns x.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.always(7)%0A%0Aconst%20result%20%3D%20fn()%0A%2F%2F%20%3D%3E%207">Try this <strong>R.always</strong> example in Rambda REPL</a>

and

Logical AND

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.and(true%2C%20true)%3B%20%2F%2F%20%3D%3E%20true%0AR.and(false%2C%20true)%3B%20%2F%2F%20%3D%3E%20false%0Aconst%20result%20%3D%20R.and(true%2C%20'foo')%3B%20%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.and</strong> example in Rambda REPL</a>

any

any<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if at least one member of list returns true, when passed to a predicate function.

const list = [1, 2, 3]
const predicate = x => x * x > 8
R.any(fn, list)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20*%20x%20%3E%208%0Aconst%20result%20%3D%20R.any(fn%2C%20list)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.any</strong> example in Rambda REPL</a>

export function any(predicate, list){
  if (arguments.length === 1) return _list => any(predicate, _list)

  let counter = 0
  while (counter < list.length){
    if (predicate(list[ counter ], counter)){
      return true
    }
    counter++
  }

  return false
}

import { any } from './any.js'

const list = [ 1, 2, 3 ]

test('happy', () => {
  expect(any(x => x < 0, list)).toBeFalse()
})

test('with curry', () => {
  expect(any(x => x > 2)(list)).toBeTrue()
})

anyFalse

anyFalse(...input: any[]): boolean

It returns true if any of inputs is falsy(empty objects and empty arrays are considered falsy).

R.anyFalse(1, {a: 1}, [1], () => false)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.anyFalse(1%2C%20%7Ba%3A%201%7D%2C%20%5B1%5D%2C%20()%20%3D%3E%20false)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.anyFalse</strong> example in Rambda REPL</a>

import { isFalsy } from './_internals/isFalsy.js'
import { type } from './type.js'

export function anyFalse(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isFalsy(x())){
        return true
      }
    } else if (isFalsy(x)){
      return true
    }

    counter++
  }

  return false
}

import { anyFalse } from './anyFalse.js'

test('when true', () => {
  expect(anyFalse(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyFalse(true, true)).toBeFalsy()
})

test('supports function', () => {
  expect(anyFalse(
    true,
    () => true,
    () => false
  )).toBeTruthy()
})

anyPass

anyPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It accepts list of predicates and returns a function. This function with its input will return true, if any of predicates returns true for this input.

const isBig = x => x > 20
const isOdd = x => x % 2 === 1
const input = 11

const fn = R.anyPass(
  [isBig, isOdd]
)

const result = fn(input) 
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20isBig%20%3D%20x%20%3D%3E%20x%20%3E%2020%0Aconst%20isOdd%20%3D%20x%20%3D%3E%20x%20%25%202%20%3D%3D%3D%201%0Aconst%20input%20%3D%2011%0A%0Aconst%20fn%20%3D%20R.anyPass(%0A%20%20%5BisBig%2C%20isOdd%5D%0A)%0A%0Aconst%20result%20%3D%20fn(input)%20%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.anyPass</strong> example in Rambda REPL</a>

export function anyPass(predicates){
  return (...input) => {
    let counter = 0
    while (counter < predicates.length){
      if (predicates[ counter ](...input)){
        return true
      }
      counter++
    }

    return false
  }
}

import { anyPass } from './anyPass.js'

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]
  const predicate = anyPass(rules)
  expect(predicate('foo')).toBeTrue()
  expect(predicate(6)).toBeFalse()
})

test('happy', () => {
  const rules = [ x => typeof x === 'string', x => x > 10 ]

  expect(anyPass(rules)(11)).toBeTrue()
  expect(anyPass(rules)(undefined)).toBeFalse()
})

const obj = {
  a : 1,
  b : 2,
}

test('when returns true', () => {
  const conditionArr = [ val => val.a === 1, val => val.a === 2 ]

  expect(anyPass(conditionArr)(obj)).toBeTrue()
})

test('when returns false + curry', () => {
  const conditionArr = [ val => val.a === 2, val => val.b === 3 ]

  expect(anyPass(conditionArr)(obj)).toBeFalse()
})

test('with empty predicates list', () => {
  expect(anyPass([])(3)).toBeFalse()
})

test('works with multiple inputs', () => {
  const fn = function (
    w, x, y, z
  ){
    console.log(
      w, x, y, z
    )

    return w + x === y + z
  }
  expect(anyPass([ fn ])(
    3, 3, 3, 3
  )).toBeTrue()
})

anyTrue

anyTrue(...input: any[]): boolean

It returns true if any of inputs arguments are truthy(empty objects and empty arrays are considered falsy).

R.anyTrue(0, null, [], {}, '', () => true)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.anyTrue(0%2C%20null%2C%20%5B%5D%2C%20%7B%7D%2C%20''%2C%20()%20%3D%3E%20true)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.anyTrue</strong> example in Rambda REPL</a>

import { isTruthy } from './_internals/isTruthy.js'
import { type } from './type.js'

export function anyTrue(...inputs){
  let counter = 0
  while (counter < inputs.length){
    const x = inputs[ counter ]

    if (type(x) === 'Function'){
      if (isTruthy(x())){
        return true
      }
    } else if (isTruthy(x)){
      return true
    }

    counter++
  }

  return false
}

import { anyTrue } from './anyTrue.js'

test('when true', () => {
  expect(anyTrue(
    true, true, false
  )).toBeTruthy()
})

test('when false', () => {
  expect(anyTrue(
    false, false, false
  )).toBeFalsy()
})

test('supports function', () => {
  expect(anyTrue(
    false,
    false,
    false,
    () => false,
    () => true
  )).toBeTruthy()
})

anyType

anyType(targetType: RambdaTypes): (...input: any[]) => boolean

It returns a function which will return true if at least one of its inputs arguments belongs to targetType.

targetType is one of the possible returns of R.type

:boom: targetType is one of the possible returns of R.type

const targetType = 'String'

const result = R.anyType(
  targetType
)(1, {}, 'foo')
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20targetType%20%3D%20'String'%0A%0Aconst%20result%20%3D%20R.anyType(%0A%20%20targetType%0A)(1%2C%20%7B%7D%2C%20'foo')%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.anyType</strong> example in Rambda REPL</a>

import { type } from './type.js'

export function anyType(targetType){
  return (...inputs) => {
    let counter = 0

    while (counter < inputs.length){
      if (type(inputs[ counter ]) === targetType){
        return true
      }
      counter++
    }

    return false
  }
}

import { anyType } from './anyType.js'

test('when true', () => {
  const result = anyType('Array')(
    1, undefined, null, []
  )

  expect(result).toBeTrue()
})

test('when false', () => {
  const result = anyType('String')(
    1, undefined, null, []
  )

  expect(result).toBeFalse()
})

ap

ap<T, U>(fns: Array<(a: T) => U>[], vs: T[]): U[]

It takes a list of functions and a list of values. Then it returns a list of values obtained by applying each function to each value.

const result = R.ap(
  [
    x => x + 1,
    x => x + 2,
  ],
  [1, 2, 3]
)
// => [2, 3, 4, 3, 4, 5]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.ap(%0A%20%20%5B%0A%20%20%20%20x%20%3D%3E%20x%20%2B%201%2C%0A%20%20%20%20x%20%3D%3E%20x%20%2B%202%2C%0A%20%20%5D%2C%0A%20%20%5B1%2C%202%2C%203%5D%0A)%0A%2F%2F%20%3D%3E%20%5B2%2C%203%2C%204%2C%203%2C%204%2C%205%5D">Try this <strong>R.ap</strong> example in Rambda REPL</a>

export function ap(functions, input){
  if (arguments.length === 1){
    return _inputs => ap(functions, _inputs)
  }

  return functions.reduce((acc, fn) => [ ...acc, ...input.map(fn) ], [])
}

import { ap } from './ap.js'

function mult2(x){
  return x * 2
}
function plus3(x){
  return x + 3
}

test('happy', () => {
  expect(ap([ mult2, plus3 ], [ 1, 2, 3 ])).toEqual([ 2, 4, 6, 4, 5, 6 ])
})

aperture

aperture<N extends number, T>(n: N, list: T[]): Array<Tuple<T, N>> | []

It returns a new list, composed of consecutive n-tuples from a list.

const result = R.aperture(2, [1, 2, 3, 4])
// => [[1, 2], [2, 3], [3, 4]]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.aperture(2%2C%20%5B1%2C%202%2C%203%2C%204%5D)%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%202%5D%2C%20%5B2%2C%203%5D%2C%20%5B3%2C%204%5D%5D">Try this <strong>R.aperture</strong> example in Rambda REPL</a>

export function aperture(step, list){
  if (arguments.length === 1){
    return _list => aperture(step, _list)
  }
  if (step > list.length) return []
  let idx = 0
  const limit = list.length - (step - 1)
  const acc = new Array(limit)
  while (idx < limit){
    acc[ idx ] = list.slice(idx, idx + step)
    idx += 1
  }

  return acc
}

import { aperture } from './aperture.js'

const list = [ 1, 2, 3, 4, 5, 6, 7 ]

test('happy', () => {
  expect(aperture(1, list)).toEqual([ [ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ] ])
  expect(aperture(2, list)).toEqual([
    [ 1, 2 ],
    [ 2, 3 ],
    [ 3, 4 ],
    [ 4, 5 ],
    [ 5, 6 ],
    [ 6, 7 ],
  ])
  expect(aperture(3, list)).toEqual([
    [ 1, 2, 3 ],
    [ 2, 3, 4 ],
    [ 3, 4, 5 ],
    [ 4, 5, 6 ],
    [ 5, 6, 7 ],
  ])
  expect(aperture(8, list)).toEqual([])
})

append

append<T>(xToAppend: T, iterable: T[]): T[]

It adds element x at the end of iterable.

const x = 'foo'

const result = R.append(x, ['bar', 'baz'])
// => ['bar', 'baz', 'foo']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%20'foo'%0A%0Aconst%20result%20%3D%20R.append(x%2C%20%5B'bar'%2C%20'baz'%5D)%0A%2F%2F%20%3D%3E%20%5B'bar'%2C%20'baz'%2C%20'foo'%5D">Try this <strong>R.append</strong> example in Rambda REPL</a>

import { cloneList } from './_internals/cloneList.js'

export function append(x, input){
  if (arguments.length === 1) return _input => append(x, _input)

  if (typeof input === 'string') return input.split('').concat(x)

  const clone = cloneList(input)
  clone.push(x)

  return clone
}

import { append } from './append.js'

test('happy', () => {
  expect(append('tests', [ 'write', 'more' ])).toEqual([
    'write',
    'more',
    'tests',
  ])
})

test('append to empty array', () => {
  expect(append('tests')([])).toEqual([ 'tests' ])
})

test('with strings', () => {
  expect(append('o', 'fo')).toEqual([ 'f', 'o', 'o' ])
})

apply

apply<T = any>(fn: (...args: any[]) => T, args: any[]): T

It applies function fn to the list of arguments.

This is useful for creating a fixed-arity function from a variadic function. fn should be a bound function if context is significant.

const result = R.apply(Math.max, [42, -Infinity, 1337])
// => 1337

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.apply(Math.max%2C%20%5B42%2C%20-Infinity%2C%201337%5D)%0A%2F%2F%20%3D%3E%201337">Try this <strong>R.apply</strong> example in Rambda REPL</a>

export function apply(fn, args){
  if (arguments.length === 1){
    return _args => apply(fn, _args)
  }

  return fn.apply(this, args)
}

import { apply } from './apply.js'
import { bind } from './bind.js'
import { identity } from './identity.js'

test('happy', () => {
  expect(apply(identity, [ 1, 2, 3 ])).toBe(1)
})

test('applies function to argument list', () => {
  expect(apply(Math.max, [ 1, 2, 3, -99, 42, 6, 7 ])).toBe(42)
})

test('provides no way to specify context', () => {
  const obj = {
    method (){
      return this === obj
    },
  }
  expect(apply(obj.method, [])).toBeFalse()
  expect(apply(bind(obj.method, obj), [])).toBeTrue()
})

applyDiff

applyDiff<Output>(rules: ApplyDiffRule[], obj: object): Output

It changes paths in an object according to a list of operations. Valid operations are add, update and delete. Its use-case is while writing tests and you need to change the test data.

Note, that you cannot use update operation, if the object path is missing in the input object. Also, you cannot use add operation, if the object path has a value.

const obj = {a: {b:1, c:2}}
const rules = [
  {op: 'remove', path: 'a.c'},
  {op: 'add', path: 'a.d', value: 4},
  {op: 'update', path: 'a.b', value: 2},
]
const result = R.applyDiff(rules, Record<string, unknown>)
const expected = {a: {b: 2, d: 4}}

// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%20%7Bb%3A1%2C%20c%3A2%7D%7D%0Aconst%20rules%20%3D%20%5B%0A%20%20%7Bop%3A%20'remove'%2C%20path%3A%20'a.c'%7D%2C%0A%20%20%7Bop%3A%20'add'%2C%20path%3A%20'a.d'%2C%20value%3A%204%7D%2C%0A%20%20%7Bop%3A%20'update'%2C%20path%3A%20'a.b'%2C%20value%3A%202%7D%2C%0A%5D%0Aconst%20result%20%3D%20R.applyDiff(rules%2C%20Record%3Cstring%2C%20unknown%3E)%0Aconst%20expected%20%3D%20%7Ba%3A%20%7Bb%3A%202%2C%20d%3A%204%7D%7D%0A%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.applyDiff</strong> example in Rambda REPL</a>

import { createPath } from './_internals/createPath.js'
import { assocPathFn } from './assocPath.js'
import { path as pathModule } from './path.js'
const ALLOWED_OPERATIONS = [ 'remove', 'add', 'update' ]

export function removeAtPath(path, obj){
  const p = createPath(path)

  const len = p.length
  if (len === 0) return
  if (len === 1) return delete obj[ p[ 0 ] ]
  if (len === 2) return delete obj[ p[ 0 ] ][ p[ 1 ] ]
  if (len === 3) return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ]
  if (len === 4) return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ]
  if (len === 5) return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ]
  if (len === 6)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ]

  if (len === 7)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ]

  if (len === 8)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ][ p[ 7 ] ]

  if (len === 9)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ][ p[ 7 ] ][ p[ 8 ] ]

  if (len === 10)
    return delete obj[ p[ 0 ] ][ p[ 1 ] ][ p[ 2 ] ][ p[ 3 ] ][ p[ 4 ] ][ p[ 5 ] ][ p[ 6 ] ][ p[ 7 ] ][ p[ 8 ] ][
      p[ 9 ]
    ]

}

export function applyDiff(rules, obj){
  if (arguments.length === 1) return _obj => applyDiff(rules, _obj)

  let clone = { ...obj }

  rules.forEach(({ op, path, value }) => {
    if (!ALLOWED_OPERATIONS.includes(op)) return
    if (op === 'add' && path && value !== undefined){
      if (pathModule(path, obj)) return

      clone = assocPathFn(
        path, value, clone
      )

      return
    }

    if (op === 'remove'){
      if (pathModule(path, obj) === undefined) return

      removeAtPath(path, clone)

      return
    }
    if (op === 'update' && path && value !== undefined){
      if (pathModule(path, obj) === undefined) return

      clone = assocPathFn(
        path, value, clone
      )

    }
  })

  return clone
}

import { applyDiff } from './applyDiff.js'

test('remove operation', () => {
  const rules = [
    {
      op   : 'remove',
      path : 'a.b',
    },
  ]
  const result = applyDiff(rules, {
    a : {
      b : 1,
      c : 2,
    },
  })
  expect(result).toEqual({ a : { c : 2 } })
})

test('update operation', () => {
  const rules = [
    {
      op    : 'update',
      path  : 'a.b',
      value : 3,
    },
    {
      op    : 'update',
      path  : 'a.c.1',
      value : 3,
    },
    {
      op    : 'update',
      path  : 'a.d',
      value : 3,
    },
  ]
  expect(applyDiff(rules, {
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  })).toEqual({
    a : {
      b : 3,
      c : [ 1, 3 ],
    },
  })
})

test('add operation', () => {
  const rules = [
    {
      op    : 'add',
      path  : 'a.b',
      value : 3,
    },
    {
      op    : 'add',
      path  : 'a.d',
      value : 3,
    },
  ]
  const result = applyDiff(rules, {
    a : {
      b : 1,
      c : 2,
    },
  })

  expect(result).toEqual({
    a : {
      b : 1,
      c : 2,
      d : 3,
    },
  })
})

applySpec

applySpec<Spec extends Record<string, AnyFunction>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }

:boom: The currying in this function works best with functions with 4 arguments or less. (arity of 4)

const fn = R.applySpec({
  sum: R.add,
  nested: { mul: R.multiply }
})
const result = fn(2, 4) 
// => { sum: 6, nested: { mul: 8 } }

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.applySpec(%7B%0A%20%20sum%3A%20R.add%2C%0A%20%20nested%3A%20%7B%20mul%3A%20R.multiply%20%7D%0A%7D)%0Aconst%20result%20%3D%20fn(2%2C%204)%20%0A%2F%2F%20%3D%3E%20%7B%20sum%3A%206%2C%20nested%3A%20%7B%20mul%3A%208%20%7D%20%7D">Try this <strong>R.applySpec</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

// recursively traverse the given spec object to find the highest arity function
export function __findHighestArity(spec, max = 0){
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    if (typeof spec[ key ] === 'object'){
      max = Math.max(max, __findHighestArity(spec[ key ]))
    }

    if (typeof spec[ key ] === 'function'){
      max = Math.max(max, spec[ key ].length)
    }
  }

  return max
}

function __filterUndefined(){
  const defined = []
  let i = 0
  const l = arguments.length
  while (i < l){
    if (typeof arguments[ i ] === 'undefined') break
    defined[ i ] = arguments[ i ]
    i++
  }

  return defined
}

function __applySpecWithArity(
  spec, arity, cache
){
  const remaining = arity - cache.length

  if (remaining === 1)
    return x =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, x)
      )
  if (remaining === 2)
    return (x, y) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y
        )
      )
  if (remaining === 3)
    return (
      x, y, z
    ) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(
          ...cache, x, y, z
        )
      )
  if (remaining === 4)
    return (
      x, y, z, a
    ) =>
      __applySpecWithArity(
        spec,
        arity,
        __filterUndefined(
          ...cache, x, y, z, a
        )
      )
  if (remaining > 4)
    return (...args) =>
      __applySpecWithArity(
        spec, arity, __filterUndefined(...cache, ...args)
      )

  // handle spec as Array
  if (isArray(spec)){
    const ret = []
    let i = 0
    const l = spec.length
    for (; i < l; i++){
      // handle recursive spec inside array
      if (typeof spec[ i ] === 'object' || isArray(spec[ i ])){
        ret[ i ] = __applySpecWithArity(
          spec[ i ], arity, cache
        )
      }
      // apply spec to the key
      if (typeof spec[ i ] === 'function'){
        ret[ i ] = spec[ i ](...cache)
      }
    }

    return ret
  }

  // handle spec as Object
  const ret = {}
  // apply callbacks to each property in the spec object
  for (const key in spec){
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    // apply the spec recursively
    if (typeof spec[ key ] === 'object'){
      ret[ key ] = __applySpecWithArity(
        spec[ key ], arity, cache
      )
      continue
    }

    // apply spec to the key
    if (typeof spec[ key ] === 'function'){
      ret[ key ] = spec[ key ](...cache)
    }
  }

  return ret
}

export function applySpec(spec, ...args){
  // get the highest arity spec function, cache the result and pass to __applySpecWithArity
  const arity = __findHighestArity(spec)

  if (arity === 0){
    return () => ({})
  }
  const toReturn = __applySpecWithArity(
    spec, arity, args
  )

  return toReturn
}

import { applySpec as applySpecRamda, nAry } from 'ramda'

import {
  add,
  always,
  compose,
  dec,
  inc,
  map,
  path,
  prop,
  T,
} from '../rambda.js'
import { applySpec } from './applySpec.js'

test('different than Ramda when bad spec', () => {
  const result = applySpec({ sum : { a : 1 } })(1, 2)
  const ramdaResult = applySpecRamda({ sum : { a : 1 } })(1, 2)
  expect(result).toEqual({})
  expect(ramdaResult).toEqual({ sum : { a : {} } })
})

test('works with empty spec', () => {
  expect(applySpec({})()).toEqual({})
  expect(applySpec([])(1, 2)).toEqual({})
  expect(applySpec(null)(1, 2)).toEqual({})
})

test('works with unary functions', () => {
  const result = applySpec({
    v : inc,
    u : dec,
  })(1)
  const expected = {
    v : 2,
    u : 0,
  }
  expect(result).toEqual(expected)
})

test('works with binary functions', () => {
  const result = applySpec({ sum : add })(1, 2)
  expect(result).toEqual({ sum : 3 })
})

test('works with nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : { sum : add },
  })(1, 2)
  const expected = {
    unnested : 0,
    nested   : { sum : 3 },
  }
  expect(result).toEqual(expected)
})

test('works with arrays of nested specs', () => {
  const result = applySpec({
    unnested : always(0),
    nested   : [ { sum : add } ],
  })(1, 2)

  expect(result).toEqual({
    unnested : 0,
    nested   : [ { sum : 3 } ],
  })
})

test('works with arrays of spec objects', () => {
  const result = applySpec([ { sum : add } ])(1, 2)

  expect(result).toEqual([ { sum : 3 } ])
})

test('works with arrays of functions', () => {
  const result = applySpec([ map(prop('a')), map(prop('b')) ])([
    {
      a : 'a1',
      b : 'b1',
    },
    {
      a : 'a2',
      b : 'b2',
    },
  ])
  const expected = [
    [ 'a1', 'a2' ],
    [ 'b1', 'b2' ],
  ]
  expect(result).toEqual(expected)
})

test('works with a spec defining a map key', () => {
  expect(applySpec({ map : prop('a') })({ a : 1 })).toEqual({ map : 1 })
})

test('cannot retains the highest arity', () => {
  const f = applySpec({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  const fRamda = applySpecRamda({
    f1 : nAry(2, T),
    f2 : nAry(5, T),
  })
  expect(f).toHaveLength(0)
  expect(fRamda).toHaveLength(5)
})

test('returns a curried function', () => {
  expect(applySpec({ sum : add })(1)(2)).toEqual({ sum : 3 })
})

// Additional tests
// ============================================
test('arity', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(
    spec, 1, 2, 3
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('arity over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(
    spec, 1, 2, 3, 4, 5
  )).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('curried', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
  }
  expect(applySpec(spec)(1)(2)(3)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
  })
})

test('curried over 5 arguments', () => {
  const spec = {
    one   : x1 => x1,
    two   : (x1, x2) => x1 + x2,
    three : (
      x1, x2, x3
    ) => x1 + x2 + x3,
    four : (
      x1, x2, x3, x4
    ) => x1 + x2 + x3 + x4,
    five : (
      x1, x2, x3, x4, x5
    ) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({
    one   : 1,
    two   : 3,
    three : 6,
    four  : 10,
    five  : 15,
  })
})

test('undefined property', () => {
  const spec = { prop : path([ 'property', 'doesnt', 'exist' ]) }
  expect(applySpec(spec, {})).toEqual({ prop : undefined })
})

test('restructure json object', () => {
  const spec = {
    id          : path('user.id'),
    name        : path('user.firstname'),
    profile     : path('user.profile'),
    doesntExist : path('user.profile.doesntExist'),
    info        : { views : compose(inc, prop('views')) },
    type        : always('playa'),
  }

  const data = {
    user : {
      id        : 1337,
      firstname : 'john',
      lastname  : 'shaft',
      profile   : 'shaft69',
    },
    views : 42,
  }

  expect(applySpec(spec, data)).toEqual({
    id          : 1337,
    name        : 'john',
    profile     : 'shaft69',
    doesntExist : undefined,
    info        : { views : 43 },
    type        : 'playa',
  })
})

applyTo

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.applyTo(%0A%20%201%2C%0A%20%20x%20%3D%3E%20x%20%2B%201%0A)%0A%2F%2F%20%3D%3E%202">Try this <strong>R.applyTo</strong> example in Rambda REPL</a>

ascend

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sort(R.descend(x%20%3D%3E%20x)%2C%20%5B2%2C%201%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.ascend</strong> example in Rambda REPL</a>

assoc

It makes a shallow clone of obj with setting or overriding the property prop with newValue.

:boom: This copies and flattens prototype properties onto the new object as well. All non-primitive properties are copied by reference.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.assoc('c'%2C%203%2C%20%7Ba%3A%201%2C%20b%3A%202%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D">Try this <strong>R.assoc</strong> example in Rambda REPL</a>

assocPath

assocPath<Output>(path: Path, newValue: any, obj: object): Output

It makes a shallow clone of obj with setting or overriding with newValue the property found with path.

const path = 'b.c'
const newValue = 2
const obj = { a: 1 }

const result = R.assocPath(path, newValue, obj)
// => { a : 1, b : { c : 2 }}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20path%20%3D%20'b.c'%0Aconst%20newValue%20%3D%202%0Aconst%20obj%20%3D%20%7B%20a%3A%201%20%7D%0A%0Aconst%20result%20%3D%20R.assocPath(path%2C%20newValue%2C%20obj)%0A%2F%2F%20%3D%3E%20%7B%20a%20%3A%201%2C%20b%20%3A%20%7B%20c%20%3A%202%20%7D%7D">Try this <strong>R.assocPath</strong> example in Rambda REPL</a>

import { cloneList } from './_internals/cloneList.js'
import { createPath } from './_internals/createPath.js'
import { isArray } from './_internals/isArray.js'
import { isIndexInteger } from './_internals/isInteger.js'
import { assocFn } from './assoc.js'
import { curry } from './curry.js'

export function assocPathFn(
  path, newValue, input
){
  const pathArrValue = createPath(path)
  if (pathArrValue.length === 0) return newValue

  const index = pathArrValue[ 0 ]
  if (pathArrValue.length > 1){
    const condition =
      typeof input !== 'object' ||
      input === null ||
      !input.hasOwnProperty(index)

    const nextInput = condition ?
      isIndexInteger(pathArrValue[ 1 ]) ?
        [] :
        {} :
      input[ index ]

    newValue = assocPathFn(
      Array.prototype.slice.call(pathArrValue, 1),
      newValue,
      nextInput
    )
  }

  if (isIndexInteger(index) && isArray(input)){
    const arr = cloneList(input)
    arr[ index ] = newValue

    return arr
  }

  return assocFn(
    index, newValue, input
  )
}

export const assocPath = curry(assocPathFn)

import { assocPathFn } from './assocPath.js'

test('happy', () => {
  const path = 'a.c.1'
  const input = {
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  }
  assocPathFn(
    path, 3, input
  )
  expect(input).toEqual({
    a : {
      b : 1,
      c : [ 1, 2 ],
    },
  })
})

test('string can be used as path input', () => {
  const testObj = {
    a : [ { b : 1 }, { b : 2 } ],
    d : 3,
  }
  const result1 = assocPathFn(
    [ 'a', 0, 'b' ], 10, testObj
  )
  const result2 = assocPathFn(
    'a.0.b', 10, testObj
  )

  const expected = {
    a : [ { b : 10 }, { b : 2 } ],
    d : 3,
  }
  expect(result1).toEqual(expected)
  expect(result2).toEqual(expected)
})

test('difference with ramda - doesn\'t overwrite primitive values with keys in the path', () => {
  const obj = { a : 'str' }
  const result = assocPathFn(
    [ 'a', 'b' ], 42, obj
  )

  expect(result).toEqual({
    a : {
      0 : 's',
      1 : 't',
      2 : 'r',
      b : 42,
    },
  })
})

test('adds a key to an empty object', () => {
  expect(assocPathFn(
    [ 'a' ], 1, {}
  )).toEqual({ a : 1 })
})

test('adds a key to a non-empty object', () => {
  expect(assocPathFn(
    'b', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object', () => {
  expect(assocPathFn(
    'b.c', 2, { a : 1 }
  )).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('adds a nested key to a nested non-empty object', () => {
  expect(assocPathFn('b.d',
    3,{
    a : 1,
    b : { c : 2 },
  })).toEqual({
    a : 1,
    b : {
      c : 2,
      d : 3,
    },
  })
})

test('adds a key to a non-empty object', () => {
  expect(assocPathFn('b', 2, { a : 1 })).toEqual({
    a : 1,
    b : 2,
  })
})

test('adds a nested key to a non-empty object', () => {
  expect(assocPathFn('b.c', 2, { a : 1 })).toEqual({
    a : 1,
    b : { c : 2 },
  })
})

test('changes an existing key', () => {
  expect(assocPathFn(
    'a', 2, { a : 1 }
  )).toEqual({ a : 2 })
})

test('undefined is considered an empty object', () => {
  expect(assocPathFn(
    'a', 1, undefined
  )).toEqual({ a : 1 })
})

test('null is considered an empty object', () => {
  expect(assocPathFn(
    'a', 1, null
  )).toEqual({ a : 1 })
})

test('value can be null', () => {
  expect(assocPathFn(
    'a', null, null
  )).toEqual({ a : null })
})

test('value can be undefined', () => {
  expect(assocPathFn(
    'a', undefined, null
  )).toEqual({ a : undefined })
})

test('assignment is shallow', () => {
  expect(assocPathFn(
    'a', { b : 2 }, { a : { c : 3 } }
  )).toEqual({ a : { b : 2 } })
})

test('empty array as path', () => {
  const result = assocPathFn(
    [], 3, {
      a : 1,
      b : 2,
    }
  )
  expect(result).toBe(3)
})

test('happy', () => {
  const expected = { foo : { bar : { baz : 42 } } }
  const result = assocPathFn(
    [ 'foo', 'bar', 'baz' ], 42, { foo : null }
  )
  expect(result).toEqual(expected)
})

binary

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.binary(%0A%20%20(a%2C%20b%2C%20c)%20%3D%3E%20a%20%2B%20b%20%2B%20c%2C%0A)(1%2C%202%2C%203%2C%204)%0A%2F%2F%20%3D%3E%203">Try this <strong>R.binary</strong> example in Rambda REPL</a>

bind

bind<F extends AnyFunction, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>

Creates a function that is bound to a context.

:boom: R.bind does not provide the additional argument-binding capabilities of Function.prototype.bind.

const log = R.bind(console.log, console)
const result = R.pipe(
  R.assoc('a', 2), 
  R.tap(log), 
  R.assoc('a', 3)
)({a: 1}); 
// => result - `{a: 3}`
// => console log - `{a: 2}`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20log%20%3D%20R.bind(console.log%2C%20console)%0Aconst%20result%20%3D%20R.pipe(%0A%20%20R.assoc('a'%2C%202)%2C%20%0A%20%20R.tap(log)%2C%20%0A%20%20R.assoc('a'%2C%203)%0A)(%7Ba%3A%201%7D)%3B%20%0A%2F%2F%20%3D%3E%20result%20-%20%60%7Ba%3A%203%7D%60%0A%2F%2F%20%3D%3E%20console%20log%20-%20%60%7Ba%3A%202%7D%60">Try this <strong>R.bind</strong> example in Rambda REPL</a>

import { curryN } from './curryN.js'

export function bind(fn, thisObj){
  if (arguments.length === 1){
    return _thisObj => bind(fn, _thisObj)
  }

  return curryN(fn.length, (...args) => fn.apply(thisObj, args))
}

import { bind } from './bind.js'

function Foo(x){
  this.x = x
}
function add(x){
  return this.x + x
}
function Bar(x, y){
  this.x = x
  this.y = y
}
Bar.prototype = new Foo()
Bar.prototype.getX = function (){
  return 'prototype getX'
}

test('returns a function', () => {
  expect(typeof bind(add)(Foo)).toBe('function')
})

test('returns a function bound to the specified context object', () => {
  const f = new Foo(12)
  function isFoo(){
    return this instanceof Foo
  }
  const isFooBound = bind(isFoo, f)
  expect(isFoo()).toBeFalse()
  expect(isFooBound()).toBeTrue()
})

test('works with built-in types', () => {
  const abc = bind(String.prototype.toLowerCase, 'ABCDEFG')
  expect(typeof abc).toBe('function')
  expect(abc()).toBe('abcdefg')
})

test('works with user-defined types', () => {
  const f = new Foo(12)
  function getX(){
    return this.x
  }
  const getXFooBound = bind(getX, f)
  expect(getXFooBound()).toBe(12)
})

test('works with plain objects', () => {
  const pojso = { x : 100 }
  function incThis(){
    return this.x + 1
  }
  const incPojso = bind(incThis, pojso)
  expect(typeof incPojso).toBe('function')
  expect(incPojso()).toBe(101)
})

test('does not interfere with existing object methods', () => {
  const b = new Bar('a', 'b')
  function getX(){
    return this.x
  }
  const getXBarBound = bind(getX, b)
  expect(b.getX()).toBe('prototype getX')
  expect(getXBarBound()).toBe('a')
})

test('preserves arity', () => {
  const f0 = function (){
    return 0
  }
  const f1 = function (a){
    return a
  }
  const f2 = function (a, b){
    return a + b
  }
  const f3 = function (
    a, b, c
  ){
    return a + b + c
  }

  expect(bind(f0, {})).toHaveLength(0)
  expect(bind(f1, {})).toHaveLength(1)
  expect(bind(f2, {})).toHaveLength(2)
  expect(bind(f3, {})).toHaveLength(3)
})

both

both(pred1: Pred, pred2: Pred): Pred

It returns a function with input argument.

This function will return true, if both firstCondition and secondCondition return true when input is passed as their argument.

const firstCondition = x => x > 10
const secondCondition = x => x < 20
const fn = R.both(firstCondition, secondCondition)

const result = [fn(15), fn(30)]
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20firstCondition%20%3D%20x%20%3D%3E%20x%20%3E%2010%0Aconst%20secondCondition%20%3D%20x%20%3D%3E%20x%20%3C%2020%0Aconst%20fn%20%3D%20R.both(firstCondition%2C%20secondCondition)%0A%0Aconst%20result%20%3D%20%5Bfn(15)%2C%20fn(30)%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.both</strong> example in Rambda REPL</a>

export function both(f, g){
  if (arguments.length === 1) return _g => both(f, _g)

  return (...input) => f(...input) && g(...input)
}

import { both } from './both.js'

const firstFn = val => val > 0
const secondFn = val => val < 10

test('with curry', () => {
  expect(both(firstFn)(secondFn)(17)).toBeFalse()
})

test('without curry', () => {
  expect(both(firstFn, secondFn)(7)).toBeTrue()
})

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = both(between, total20)
  expect(fn(
    5, 7, 8
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return false
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  both(F, Z)()

  expect(effect).toBe('not evaluated')
})

call

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.call(%0A%20%20(a%2C%20b)%20%3D%3E%20a%20%2B%20b%2C%0A%20%201%2C%0A%20%202%0A)%0A%2F%2F%20%3D%3E%203">Try this <strong>R.call</strong> example in Rambda REPL</a>

chain

chain<T, U>(fn: (n: T) => U[], list: T[]): U[]

The method is also known as flatMap.

const duplicate = n => [ n, n ]
const list = [ 1, 2, 3 ]

const result = chain(duplicate, list)
// => [ 1, 1, 2, 2, 3, 3 ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20duplicate%20%3D%20n%20%3D%3E%20%5B%20n%2C%20n%20%5D%0Aconst%20list%20%3D%20%5B%201%2C%202%2C%203%20%5D%0A%0Aconst%20result%20%3D%20chain(duplicate%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%201%2C%201%2C%202%2C%202%2C%203%2C%203%20%5D">Try this <strong>R.chain</strong> example in Rambda REPL</a>

export function chain(fn, list){
  if (arguments.length === 1){
    return _list => chain(fn, _list)
  }

  return [].concat(...list.map(fn))
}

import { chain as chainRamda } from 'ramda'

import { chain } from './chain.js'

const duplicate = n => [ n, n ]

test('happy', () => {
  const fn = x => [ x * 2 ]
  const list = [ 1, 2, 3 ]

  const result = chain(fn, list)

  expect(result).toEqual([ 2, 4, 6 ])
})

test('maps then flattens one level', () => {
  expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('maps then flattens one level - curry', () => {
  expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})

test('flattens only one level', () => {
  const nest = n => [ [ n ] ]
  expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])
})

test('can compose', () => {
  function dec(x){
    return [ x - 1 ]
  }
  function times2(x){
    return [ x * 2 ]
  }

  const mdouble = chain(times2)
  const mdec = chain(dec)
  expect(mdec(mdouble([ 10, 20, 30 ]))).toEqual([ 19, 39, 59 ])
})

test('@types/ramda broken test', () => {
  const score = {
    maths   : 90,
    physics : 80,
  }

  const calculateTotal = score => {
    const { maths, physics } = score

    return maths + physics
  }

  const assocTotalToScore = (total, score) => ({
    ...score,
    total,
  })

  const calculateAndAssocTotalToScore = chainRamda(assocTotalToScore,
    calculateTotal)
  expect(() =>
    calculateAndAssocTotalToScore(score)).toThrowErrorMatchingInlineSnapshot('"fn(...) is not a function"')
})

clamp

Restrict a number input to be within min and max limits.

If input is bigger than max, then the result is max.

If input is smaller than min, then the result is min.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.clamp(0%2C%2010%2C%205)%2C%20%0A%20%20R.clamp(0%2C%2010%2C%20-1)%2C%0A%20%20R.clamp(0%2C%2010%2C%2011)%0A%5D%0A%2F%2F%20%3D%3E%20%5B5%2C%200%2C%2010%5D">Try this <strong>R.clamp</strong> example in Rambda REPL</a>

clone

It creates a deep copy of the input, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.

:boom: It doesn't work with very specific types, such as MongoDB's ObjectId.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20objects%20%3D%20%5B%7Ba%3A%201%7D%2C%20%7Bb%3A%202%7D%5D%3B%0Aconst%20objectsClone%20%3D%20R.clone(objects)%3B%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.equals(objects%2C%20objectsClone)%2C%0A%20%20R.equals(objects%5B0%5D%2C%20objectsClone%5B0%5D)%2C%0A%5D%20%2F%2F%20%3D%3E%20%5B%20true%2C%20true%20%5D">Try this <strong>R.clone</strong> example in Rambda REPL</a>

collectBy

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.collectBy(%0A%20%20x%20%3D%3E%20x%20%25%202%2C%0A%20%20%5B1%2C%202%2C%203%2C%204%5D%0A)%0A%2F%2F%20%3D%3E%20%5B%5B2%2C%204%5D%2C%20%5B1%2C%203%5D%5D">Try this <strong>R.collectBy</strong> example in Rambda REPL</a>

comparator

It returns a comparator function that can be used in sort method.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sort(%0A%20%20R.comparator((a%2C%20b)%20%3D%3E%20a.x%20%3C%20b.x)%2C%0A%20%20%5B%7Bx%3A%202%7D%2C%20%7Bx%3A%201%7D%5D%0A)%0A%2F%2F%20%3D%3E%20%5B%7Bx%3A%201%7D%2C%20%7Bx%3A%202%7D%5D">Try this <strong>R.comparator</strong> example in Rambda REPL</a>

complement

It returns inverted version of origin function that accept input as argument.

The return value of inverted is the negative boolean value of origin(input).

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20origin%20%3D%20x%20%3D%3E%20x%20%3E%205%0Aconst%20inverted%20%3D%20complement(origin)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20origin(7)%2C%0A%20%20inverted(7)%0A%5D%20%3D%3E%20%5B%20true%2C%20false%20%5D">Try this <strong>R.complement</strong> example in Rambda REPL</a>

compose

It performs right-to-left function composition.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.compose(%0A%20%20R.map(x%20%3D%3E%20x%20*%202)%2C%0A%20%20R.filter(x%20%3D%3E%20x%20%3E%202)%0A)(%5B1%2C%202%2C%203%2C%204%5D)%0A%0A%2F%2F%20%3D%3E%20%5B6%2C%208%5D">Try this <strong>R.compose</strong> example in Rambda REPL</a>

composeAsync

Asynchronous version of R.compose. awaits the result of each function before passing it to the next. Returns a Promise of the result.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20add%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20%2B%201%0A%7D%0Aconst%20multiply%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20*%202%20%0A%7D%0A%0Aconst%20result%20%3D%20await%20R.composeAsync(%0A%20%20add%2C%0A%20%20multiply%0A)(1)%0A%2F%2F%20%60result%60%20resolves%20to%20%603%60">Try this <strong>R.composeAsync</strong> example in Rambda REPL</a>

composeWith

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.composeWith(%0A%20%20(fn%2C%20intermediateResult)%20%3D%3E%20fn(intermediateResult)%2C%0A%20%20%5B%0A%20%20%20%20R.map(x%20%3D%3E%20x%20%2B%201)%2C%0A%20%20%20%20R.map(x%20%3D%3E%20x%20*%202)%2C%0A%20%20%5D%0A)(%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%5B3%2C%205%2C%207%5D">Try this <strong>R.composeWith</strong> example in Rambda REPL</a>

concat

It returns a new string or array, which is the result of merging x and y.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.concat(%5B1%2C%202%5D)(%5B3%2C%204%5D)%20%2F%2F%20%3D%3E%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20result%20%3D%20R.concat('foo'%2C%20'bar')%20%2F%2F%20%3D%3E%20'foobar'">Try this <strong>R.concat</strong> example in Rambda REPL</a>

cond

It takes list with conditions and returns a new function fn that expects input as argument.

This function will start evaluating the conditions in order to find the first winner(order of conditions matter).

The winner is this condition, which left side returns true when input is its argument. Then the evaluation of the right side of the winner will be the final result.

If no winner is found, then fn returns undefined.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.cond(%5B%0A%20%20%5B%20x%20%3D%3E%20x%20%3E%2025%2C%20R.always('more%20than%2025')%20%5D%2C%0A%20%20%5B%20x%20%3D%3E%20x%20%3E%2015%2C%20R.always('more%20than%2015')%20%5D%2C%0A%20%20%5B%20R.T%2C%20x%20%3D%3E%20%60%24%7Bx%7D%20is%20nothing%20special%60%20%5D%2C%0A%5D)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20fn(30)%2C%0A%20%20fn(20)%2C%0A%20%20fn(10)%2C%0A%5D%20%0A%2F%2F%20%3D%3E%20%5B'more%20than%2025'%2C%20'more%20than%2015'%2C%20'10%20is%20nothing%20special'%5D">Try this <strong>R.cond</strong> example in Rambda REPL</a>

contains

contains<T, U>(target: T, compareTo: U): boolean

It returns true if all of target object properties are R.equal to compareTo object.

const result = R.contains({a:1}, {a:1, b:2})
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.contains(%7Ba%3A1%7D%2C%20%7Ba%3A1%2C%20b%3A2%7D)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.contains</strong> example in Rambda REPL</a>

import { equals } from './equals.js'

export function contains(target, toCompare){
  if (arguments.length === 1){
    return _toCompare => contains(target, _toCompare)
  }
  let willReturn = true

  Object.keys(target).forEach(prop => {
    if (!willReturn) return
    if (
      toCompare[ prop ] === undefined ||
      !equals(target[ prop ], toCompare[ prop ])
    ){
      willReturn = false
    }
  })

  return willReturn
}

import { contains } from './contains.js'

const target = { a : 1 }
const compareTo = {
  a : 1,
  b : 2,
}

test('happy', () => {
  expect(contains(target, compareTo)).toBeTrue()
})

test('curried', () => {
  expect(contains({
    ...target,
    c : 3,
  },
  compareTo)).toBeFalse()
})

converge

Accepts a converging function and a list of branching functions and returns a new function. When invoked, this new function is applied to some arguments, each branching function is applied to those same arguments. The results of each branching function are passed as arguments to the converging function to produce the return value.

:boom: Explanation is taken from Ramda documentation

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.converge(R.multiply)(%5B%20R.add(1)%2C%20R.add(3)%20%5D)(2)%0A%2F%2F%20%3D%3E%2015">Try this <strong>R.converge</strong> example in Rambda REPL</a>

count

It counts how many times predicate function returns true, when supplied with iteration of list.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A%201%7D%2C%201%2C%20%7Ba%3A2%7D%5D%0Aconst%20result%20%3D%20R.count(x%20%3D%3E%20x.a%20!%3D%3D%20undefined%2C%20list)%0A%2F%2F%20%3D%3E%202">Try this <strong>R.count</strong> example in Rambda REPL</a>

countBy

countBy<T extends unknown>(transformFn: (x: T) => any, list: T[]): Record<string, number>

It counts elements in a list after each instance of the input list is passed through transformFn function.

const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]

const result = countBy(R.toLower, list)
const expected = { a: 2, b: 2, c: 2 }
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%20'a'%2C%20'A'%2C%20'b'%2C%20'B'%2C%20'c'%2C%20'C'%20%5D%0A%0Aconst%20result%20%3D%20countBy(R.toLower%2C%20list)%0Aconst%20expected%20%3D%20%7B%20a%3A%202%2C%20b%3A%202%2C%20c%3A%202%20%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.countBy</strong> example in Rambda REPL</a>

export function countBy(fn, list){
  if (arguments.length === 1){
    return _list => countBy(fn, _list)
  }
  const willReturn = {}

  list.forEach(item => {
    const key = fn(item)
    if (!willReturn[ key ]){
      willReturn[ key ] = 1
    } else {
      willReturn[ key ]++
    }
  })

  return willReturn
}

import { countBy } from './countBy.js'

const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]

test('happy', () => {
  const result = countBy(x => x.toLowerCase(), list)
  expect(result).toEqual({
    a : 2,
    b : 2,
    c : 2,
  })
})

curry

It expects a function as input and returns its curried version.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(a%2C%20b%2C%20c)%20%3D%3E%20a%20%2B%20b%20%2B%20c%0Aconst%20curried%20%3D%20R.curry(fn)%0Aconst%20sum%20%3D%20curried(1%2C2)%0A%0Aconst%20result%20%3D%20sum(3)%20%2F%2F%20%3D%3E%206">Try this <strong>R.curry</strong> example in Rambda REPL</a>

curryN

It returns a curried equivalent of the provided function, with the specified arity.

debounce

debounce<T, U>(fn: (input: T) => U, ms: number, immediate?: boolean): (input: T) => void

let counter = 0
const increment = () => {
  counter++
}

const debounced = R.debounce(increment, 1000)

async function fn(){
  debounced()
  await R.delay(500)
  debounced()
  await R.delay(800)
  console.log(counter) // => 0

  await R.delay(1200)
  console.log(counter) // => 1

  return counter
}
const result = await fn()
// `result` resolves to `1`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?let%20counter%20%3D%200%0Aconst%20increment%20%3D%20()%20%3D%3E%20%7B%0A%20%20counter%2B%2B%0A%7D%0A%0Aconst%20debounced%20%3D%20R.debounce(increment%2C%201000)%0A%0Aasync%20function%20fn()%7B%0A%20%20debounced()%0A%20%20await%20R.delay(500)%0A%20%20debounced()%0A%20%20await%20R.delay(800)%0A%20%20console.log(counter)%20%2F%2F%20%3D%3E%200%0A%0A%20%20await%20R.delay(1200)%0A%20%20console.log(counter)%20%2F%2F%20%3D%3E%201%0A%0A%20%20return%20counter%0A%7D%0Aconst%20result%20%3D%20await%20fn()%0A%2F%2F%20%60result%60%20resolves%20to%20%601%60">Try this <strong>R.debounce</strong> example in Rambda REPL</a>

export function debounce(
  func, ms, immediate = false
){
  let timeout

  return function (...input){
    const later = function (){
      timeout = null
      if (!immediate){
        return func.apply(null, input)
      }
    }
    const callNow = immediate && !timeout
    clearTimeout(timeout)
    timeout = setTimeout(later, ms)
    if (callNow){
      return func.apply(null, input)
    }
  }
}

import { debounce } from './debounce.js'
import { delay } from './delay.js'

test('happy', async () => {
  let counter = 0
  let aHolder

  const inc = a => {
    aHolder = a
    counter++
  }
  const incWrapped = debounce(inc, 500)

  incWrapped(1)
  expect(counter).toBe(0)

  await delay(200)

  incWrapped(2)
  expect(counter).toBe(0)

  await delay(700)
  expect(counter).toBe(1)
  expect(aHolder).toBe(2)
})

test('immediate debounce', async () => {
  let counter = 0
  const inc = () => {
    counter++
  }

  const incWrapped = debounce(
    inc, 500, true
  )
  incWrapped()
  expect(counter).toBe(1)
  await delay(200)
  incWrapped()
  expect(counter).toBe(1)
  await delay(700)
  incWrapped()
  expect(counter).toBe(2)
})

dec

It decrements a number.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dec(2)%20%2F%2F%20%3D%3E%201">Try this <strong>R.dec</strong> example in Rambda REPL</a>

defaultTo

defaultTo<T>(defaultValue: T, input: T | null | undefined): T

It returns defaultValue, if all of inputArguments are undefined, null or NaN.

Else, it returns the first truthy inputArguments instance(from left to right).

:boom: Rambda's defaultTo accept indefinite number of arguments when non curried, i.e. R.defaultTo(2, foo, bar, baz).

R.defaultTo('foo', 'bar') // => 'bar'
R.defaultTo('foo', undefined) // => 'foo'

// Important - emtpy string is not falsy value(same as Ramda)
R.defaultTo('foo', '') // => 'foo'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.defaultTo('foo'%2C%20'bar')%20%2F%2F%20%3D%3E%20'bar'%0AR.defaultTo('foo'%2C%20undefined)%20%2F%2F%20%3D%3E%20'foo'%0A%0A%2F%2F%20Important%20-%20emtpy%20string%20is%20not%20falsy%20value(same%20as%20Ramda)%0Aconst%20result%20%3D%20R.defaultTo('foo'%2C%20'')%20%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.defaultTo</strong> example in Rambda REPL</a>

function isFalsy(input){
  return (
    input === undefined || input === null || Number.isNaN(input) === true
  )
}

export function defaultTo(defaultArgument, input){
  if (arguments.length === 1){
    return _input => defaultTo(defaultArgument, _input)
  }

  return isFalsy(input) ? defaultArgument : input
}

import { defaultTo } from './defaultTo.js'

test('with undefined', () => {
  expect(defaultTo('foo')(undefined)).toBe('foo')
})

test('with null', () => {
  expect(defaultTo('foo')(null)).toBe('foo')
})

test('with NaN', () => {
  expect(defaultTo('foo')(NaN)).toBe('foo')
})

test('with empty string', () => {
  expect(defaultTo('foo', '')).toBe('')
})

test('with false', () => {
  expect(defaultTo('foo', false)).toBeFalse()
})

test('when inputArgument passes initial check', () => {
  expect(defaultTo('foo', 'bar')).toBe('bar')
})

delay

delay(ms: number): Promise<'RAMBDAX_DELAY'>

setTimeout as a promise that resolves to R.DELAY variable after ms milliseconds.

const result = R.delay(1000)
// `result` resolves to `RAMBDAX_DELAY`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.delay(1000)%0A%2F%2F%20%60result%60%20resolves%20to%20%60RAMBDAX_DELAY%60">Try this <strong>R.delay</strong> example in Rambda REPL</a>

export const DELAY = 'RAMBDAX_DELAY'

export function delay(ms){
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(DELAY)
    }, ms)
  })
}

import { DELAY, delay } from './delay.js'

test('usage with variables', async () => {
  await expect(delay(500)).resolves.toBe(DELAY)
})

descend

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sort(R.descend(x%20%3D%3E%20x)%2C%20%5B1%2C%202%5D)%0A%2F%2F%20%3D%3E%20%5B2%2C%201%5D">Try this <strong>R.descend</strong> example in Rambda REPL</a>

difference

difference<T>(a: T[], b: T[]): T[]

It returns the uniq set of all elements in the first list a not contained in the second list b.

R.equals is used to determine equality.

const a = [ 1, 2, 3, 4 ]
const b = [ 3, 4, 5, 6 ]

const result = R.difference(a, b)
// => [ 1, 2 ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20a%20%3D%20%5B%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20b%20%3D%20%5B%203%2C%204%2C%205%2C%206%20%5D%0A%0Aconst%20result%20%3D%20R.difference(a%2C%20b)%0A%2F%2F%20%3D%3E%20%5B%201%2C%202%20%5D">Try this <strong>R.difference</strong> example in Rambda REPL</a>

import { includes } from './includes.js'
import { uniq } from './uniq.js'

export function difference(a, b){
  if (arguments.length === 1) return _b => difference(a, _b)

  return uniq(a).filter(aInstance => !includes(aInstance, b))
}

import { difference as differenceRamda } from 'ramda'

import { difference } from './difference.js'

test('difference', () => {
  const a = [ 1, 2, 3, 4 ]
  const b = [ 3, 4, 5, 6 ]
  expect(difference(a)(b)).toEqual([ 1, 2 ])

  expect(difference([], [])).toEqual([])
})

test('difference with objects', () => {
  const a = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const b = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(difference(a, b)).toEqual([ { id : 1 }, { id : 2 } ])
})

test('no duplicates in first list', () => {
  const M2 = [ 1, 2, 3, 4, 1, 2, 3, 4 ]
  const N2 = [ 3, 3, 4, 4, 5, 5, 6, 6 ]
  expect(difference(M2, N2)).toEqual([ 1, 2 ])
})

test('should use R.equals', () => {
  expect(difference([ 1 ], [ 1 ])).toHaveLength(0)
  expect(differenceRamda([ NaN ], [ NaN ])).toHaveLength(0)
})

differenceWith

differenceWith<T1, T2>(
  pred: (a: T1, b: T2) => boolean,
  list1: T1[],
  list2: T2[],
): T1[]

const result = R.differenceWith(
  (a, b) => a.x === b.x,
  [{x: 1}, {x: 2}],
  [{x: 1}, {x: 3}]
)
// => [{x: 2}]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.differenceWith(%0A%20%20(a%2C%20b)%20%3D%3E%20a.x%20%3D%3D%3D%20b.x%2C%0A%20%20%5B%7Bx%3A%201%7D%2C%20%7Bx%3A%202%7D%5D%2C%0A%20%20%5B%7Bx%3A%201%7D%2C%20%7Bx%3A%203%7D%5D%0A)%0A%2F%2F%20%3D%3E%20%5B%7Bx%3A%202%7D%5D">Try this <strong>R.differenceWith</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { _indexOf } from './equals.js'

export function differenceWithFn(
  fn, a, b
){
  const willReturn = []
  const [ first, second ] = a.length >= b.length ? [ a, b ] : [ b, a ]

  first.forEach(item => {
    const hasItem = second.some(secondItem => fn(item, secondItem))
    if (!hasItem && _indexOf(item, willReturn) === -1){
      willReturn.push(item)
    }
  })

  return willReturn
}

export const differenceWith = curry(differenceWithFn)

import { differenceWith } from './differenceWith.js';

const fn = (a, b) => a.x === b.x;

test('same length of list', () => {
	const result = differenceWith(fn, [{ x: 1 }, { x: 2 }], [{ x: 1 }, { x: 3 }]);
	expect(result).toEqual([{ x: 2 }]);
});

test('different length of list', () => {
	const foo = [{ x: 1 }, { x: 2 }, { x: 3 }];
	const bar = [{ x: 3 }, { x: 4 }];
	const result = differenceWith(fn, foo, bar);
	expect(result).toEqual([{ x: 1 }, { x: 2 }]);
});

dissoc

It returns a new object that does not contain property prop.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dissoc('b'%2C%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20c%3A%203%7D">Try this <strong>R.dissoc</strong> example in Rambda REPL</a>

dissocPath

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dissocPath(%5B'a'%2C%20'b'%5D%2C%20%7Ba%3A%20%7Bb%3A%201%2C%20c%3A%202%7D%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%20%7Bc%3A%202%7D%7D">Try this <strong>R.dissocPath</strong> example in Rambda REPL</a>

divide

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.divide(71%2C%20100)%20%2F%2F%20%3D%3E%200.71">Try this <strong>R.divide</strong> example in Rambda REPL</a>

drop

drop<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from beginning of list or string input.

R.drop(2, ['foo', 'bar', 'baz']) // => ['baz']
R.drop(2, 'foobar')  // => 'obar'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.drop(2%2C%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D)%20%2F%2F%20%3D%3E%20%5B'baz'%5D%0Aconst%20result%20%3D%20R.drop(2%2C%20'foobar')%20%20%2F%2F%20%3D%3E%20'obar'">Try this <strong>R.drop</strong> example in Rambda REPL</a>

export function drop(howManyToDrop, listOrString){
  if (arguments.length === 1) return _list => drop(howManyToDrop, _list)

  return listOrString.slice(howManyToDrop > 0 ? howManyToDrop : 0)
}

import assert from 'assert'

import { drop } from './drop.js'

test('with array', () => {
  expect(drop(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])
  expect(drop(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(drop(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(drop(3, 'rambda')).toBe('bda')
})

test('with non-positive count', () => {
  expect(drop(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(drop(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(drop(0, xs), xs)
  assert.notStrictEqual(drop(-1, xs), xs)
})

dropLast

dropLast<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from the end of list or string input.

R.dropLast(2, ['foo', 'bar', 'baz']) // => ['foo']
R.dropLast(2, 'foobar')  // => 'foob'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.dropLast(2%2C%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D)%20%2F%2F%20%3D%3E%20%5B'foo'%5D%0Aconst%20result%20%3D%20R.dropLast(2%2C%20'foobar')%20%20%2F%2F%20%3D%3E%20'foob'">Try this <strong>R.dropLast</strong> example in Rambda REPL</a>

export function dropLast(howManyToDrop, listOrString){
  if (arguments.length === 1){
    return _listOrString => dropLast(howManyToDrop, _listOrString)
  }

  return howManyToDrop > 0 ?
    listOrString.slice(0, -howManyToDrop) :
    listOrString.slice()
}

import assert from 'assert'

import { dropLast } from './dropLast.js'

test('with array', () => {
  expect(dropLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo' ])
  expect(dropLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
  expect(dropLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})

test('with string', () => {
  expect(dropLast(3, 'rambda')).toBe('ram')
})

test('with non-positive count', () => {
  expect(dropLast(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(dropLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('should return copy', () => {
  const xs = [ 1, 2, 3 ]

  assert.notStrictEqual(dropLast(0, xs), xs)
  assert.notStrictEqual(dropLast(-1, xs), xs)
})

dropLastWhile

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%3B%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%3D%203%0A%0Aconst%20result%20%3D%20dropLastWhile(predicate%2C%20list)%3B%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.dropLastWhile</strong> example in Rambda REPL</a>

dropRepeats

dropRepeats<T>(list: T[]): T[]

It removes any successive duplicates according to R.equals.

const result = R.dropRepeats([
  1, 
  1, 
  {a: 1}, 
  {a:1}, 
  1
])
// => [1, {a: 1}, 1]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dropRepeats(%5B%0A%20%201%2C%20%0A%20%201%2C%20%0A%20%20%7Ba%3A%201%7D%2C%20%0A%20%20%7Ba%3A1%7D%2C%20%0A%20%201%0A%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%20%7Ba%3A%201%7D%2C%201%5D">Try this <strong>R.dropRepeats</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function dropRepeats(list){
  if (!isArray(list)){
    throw new Error(`${ list } is not a list`)
  }

  const toReturn = []

  list.reduce((prev, current) => {
    if (!equals(prev, current)){
      toReturn.push(current)
    }

    return current
  }, undefined)

  return toReturn
}

import { dropRepeats as dropRepeatsRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { add } from './add.js'
import { dropRepeats } from './dropRepeats.js'

const list = [ 1, 2, 2, 2, 3, 4, 4, 5, 5, 3, 2, 2, { a : 1 }, { a : 1 } ]
const listClean = [ 1, 2, 3, 4, 5, 3, 2, { a : 1 } ]

test('happy', () => {
  const result = dropRepeats(list)
  expect(result).toEqual(listClean)
})

const possibleLists = [
  [ add(1), async () => {}, [ 1 ], [ 1 ], [ 2 ], [ 2 ] ],
  [ add(1), add(1), add(2) ],
  [],
  1,
  /foo/g,
  Promise.resolve(1),
]

describe('brute force', () => {
  compareCombinations({
    firstInput : possibleLists,
    callback   : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 1,
          "SHOULD_NOT_THROW": 3,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 6,
        }
      `)
    },
    fn      : dropRepeats,
    fnRamda : dropRepeatsRamda,
  })
})

dropRepeatsBy

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dropRepeatsBy(%0A%20%20Math.abs%2C%0A%20%20%5B1%2C%20-1%2C%202%2C%203%2C%20-3%5D%0A)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%203%5D">Try this <strong>R.dropRepeatsBy</strong> example in Rambda REPL</a>

dropRepeatsWith

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A1%2Cb%3A2%7D%2C%20%7Ba%3A1%2Cb%3A3%7D%2C%20%7Ba%3A2%2C%20b%3A4%7D%5D%0Aconst%20result%20%3D%20R.dropRepeatsWith(R.prop('a')%2C%20list)%0A%0A%2F%2F%20%3D%3E%20%5B%7Ba%3A1%2Cb%3A2%7D%2C%20%7Ba%3A2%2C%20b%3A4%7D%5D">Try this <strong>R.dropRepeatsWith</strong> example in Rambda REPL</a>

dropWhile

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3C%203%0Aconst%20result%20%3D%20R.dropWhile(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%5B3%2C%204%5D">Try this <strong>R.dropWhile</strong> example in Rambda REPL</a>

either

either(firstPredicate: Pred, secondPredicate: Pred): Pred

It returns a new predicate function from firstPredicate and secondPredicate inputs.

This predicate function will return true, if any of the two input predicates return true.

const firstPredicate = x => x > 10
const secondPredicate = x => x % 2 === 0
const predicate = R.either(firstPredicate, secondPredicate)

const result = [
  predicate(15),
  predicate(8),
  predicate(7),
]
// => [true, true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20firstPredicate%20%3D%20x%20%3D%3E%20x%20%3E%2010%0Aconst%20secondPredicate%20%3D%20x%20%3D%3E%20x%20%25%202%20%3D%3D%3D%200%0Aconst%20predicate%20%3D%20R.either(firstPredicate%2C%20secondPredicate)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20predicate(15)%2C%0A%20%20predicate(8)%2C%0A%20%20predicate(7)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.either</strong> example in Rambda REPL</a>

export function either(firstPredicate, secondPredicate){
  if (arguments.length === 1){
    return _secondPredicate => either(firstPredicate, _secondPredicate)
  }

  return (...input) =>
    Boolean(firstPredicate(...input) || secondPredicate(...input))
}

import { either } from './either.js'

test('with multiple inputs', () => {
  const between = function (
    a, b, c
  ){
    return a < b && b < c
  }
  const total20 = function (
    a, b, c
  ){
    return a + b + c === 20
  }
  const fn = either(between, total20)
  expect(fn(
    7, 8, 5
  )).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function (){
    return true
  }
  const Z = function (){
    effect = 'Z got evaluated'
  }
  either(F, Z)()

  expect(effect).toBe('not evaluated')
})

test('case 1', () => {
  const firstFn = val => val > 0
  const secondFn = val => val * 5 > 10

  expect(either(firstFn, secondFn)(1)).toBeTrue()
})

test('case 2', () => {
  const firstFn = val => val > 0
  const secondFn = val => val === -10
  const fn = either(firstFn)(secondFn)

  expect(fn(-10)).toBeTrue()
})

empty

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.empty(%5B1%2C2%2C3%5D)%2C%20R.empty('foo')%2C%20R.empty(%7Bx%3A%201%2C%20y%3A%202%7D)%5D%0A%2F%2F%20%3D%3E%20%5B%5B%5D%2C%20''%2C%20%7B%7D%5D">Try this <strong>R.empty</strong> example in Rambda REPL</a>

endsWith

endsWith<T extends string>(question: T, str: string): boolean

When iterable is a string, then it behaves as String.prototype.endsWith. When iterable is a list, then it uses R.equals to determine if the target list ends in the same way as the given target.

const str = 'foo-bar'
const list = [{a:1}, {a:2}, {a:3}]

const result = [
  R.endsWith('bar', str),
  R.endsWith([{a:1}, {a:2}], list)
]
// => [true, true]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20str%20%3D%20'foo-bar'%0Aconst%20list%20%3D%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%2C%20%7Ba%3A3%7D%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.endsWith('bar'%2C%20str)%2C%0A%20%20R.endsWith(%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%5D%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%5D">Try this <strong>R.endsWith</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function endsWith(target, iterable){
  if (arguments.length === 1) return _iterable => endsWith(target, _iterable)

  if (typeof iterable === 'string'){
    return iterable.endsWith(target)
  }
  if (!isArray(target)) return false

  const diff = iterable.length - target.length
  let correct = true
  const filtered = target.filter((x, index) => {
    if (!correct) return false
    const result = equals(x, iterable[ index + diff ])
    if (!result) correct = false

    return result
  })

  return filtered.length === target.length
}

import { endsWith as endsWithRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { endsWith } from './endsWith.js'

test('with string', () => {
  expect(endsWith('bar', 'foo-bar')).toBeTrue()
  expect(endsWith('baz')('foo-bar')).toBeFalse()
})

test('use R.equals with array', () => {
  const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
  expect(endsWith({ a : 3 }, list)).toBeFalse(),
  expect(endsWith([ { a : 3 } ], list)).toBeTrue()
  expect(endsWith([ { a : 2 }, { a : 3 } ], list)).toBeTrue()
  expect(endsWith(list, list)).toBeTrue()
  expect(endsWith([ { a : 1 } ], list)).toBeFalse()
})

export const possibleTargets = [
  NaN,
  [ NaN ],
  /foo/,
  [ /foo/ ],
  Promise.resolve(1),
  [ Promise.resolve(1) ],
  Error('foo'),
  [ Error('foo') ],
]

export const possibleIterables = [
  [ Promise.resolve(1), Promise.resolve(2) ],
  [ /foo/, /bar/ ],
  [ NaN ],
  [ Error('foo'), Error('bar') ],
]

describe('brute force', () => {
  compareCombinations({
    fn          : endsWith,
    fnRamda     : endsWithRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 32,
        }
      `)
    },
  })
})

eqBy

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.eqBy(Math.abs%2C%205%2C%20-5)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.eqBy</strong> example in Rambda REPL</a>

eqProps

It returns true if property prop in obj1 is equal to property prop in obj2 according to R.equals.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj1%20%3D%20%7Ba%3A%201%2C%20b%3A2%7D%0Aconst%20obj2%20%3D%20%7Ba%3A%201%2C%20b%3A3%7D%0Aconst%20result%20%3D%20R.eqProps('a'%2C%20obj1%2C%20obj2)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.eqProps</strong> example in Rambda REPL</a>

equals

equals<T>(x: T, y: T): boolean

It deeply compares x and y and returns true if they are equal.

:boom: It doesn't handle cyclical data structures and functions

R.equals(
  [1, {a:2}, [{b: 3}]],
  [1, {a:2}, [{b: 3}]]
) // => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.equals(%0A%20%20%5B1%2C%20%7Ba%3A2%7D%2C%20%5B%7Bb%3A%203%7D%5D%5D%2C%0A%20%20%5B1%2C%20%7Ba%3A2%7D%2C%20%5B%7Bb%3A%203%7D%5D%5D%0Aconst%20result%20%3D%20)%20%2F%2F%20%3D%3E%20true">Try this <strong>R.equals</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { type } from './type.js'

export function _lastIndexOf(valueToFind, list){
  if (!isArray(list))
    throw new Error(`Cannot read property 'indexOf' of ${ list }`)

  const typeOfValue = type(valueToFind)
  if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
    return list.lastIndexOf(valueToFind)

  const { length } = list
  let index = length
  let foundIndex = -1

  while (--index > -1 && foundIndex === -1)
    if (equals(list[ index ], valueToFind))
      foundIndex = index

  return foundIndex
}

export function _indexOf(valueToFind, list){
  if (!isArray(list))
    throw new Error(`Cannot read property 'indexOf' of ${ list }`)

  const typeOfValue = type(valueToFind)
  if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
    return list.indexOf(valueToFind)

  let index = -1
  let foundIndex = -1
  const { length } = list

  while (++index < length && foundIndex === -1)
    if (equals(list[ index ], valueToFind))
      foundIndex = index

  return foundIndex
}

function _arrayFromIterator(iter){
  const list = []
  let next
  while (!(next = iter.next()).done)
    list.push(next.value)

  return list
}

function _compareSets(a, b){
  if (a.size !== b.size)
    return false

  const aList = _arrayFromIterator(a.values())
  const bList = _arrayFromIterator(b.values())

  const filtered = aList.filter(aInstance => _indexOf(aInstance, bList) === -1)

  return filtered.length === 0
}

function compareErrors(a, b){
  if (a.message !== b.message) return false
  if (a.toString !== b.toString) return false

  return a.toString() === b.toString()
}

function parseDate(maybeDate){
  if (!maybeDate.toDateString) return [ false ]

  return [ true, maybeDate.getTime() ]
}

function parseRegex(maybeRegex){
  if (maybeRegex.constructor !== RegExp) return [ false ]

  return [ true, maybeRegex.toString() ]
}

export function equals(a, b){
  if (arguments.length === 1) return _b => equals(a, _b)

  if (Object.is(a, b)) return true

  const aType = type(a)

  if (aType !== type(b)) return false
  if (aType === 'Function')
    return a.name === undefined ? false : a.name === b.name

  if ([ 'NaN', 'Null', 'Undefined' ].includes(aType)) return true

  if ([ 'BigInt', 'Number' ].includes(aType)){
    if (Object.is(-0, a) !== Object.is(-0, b)) return false

    return a.toString() === b.toString()
  }

  if ([ 'Boolean', 'String' ].includes(aType))
    return a.toString() === b.toString()

  if (aType === 'Array'){
    const aClone = Array.from(a)
    const bClone = Array.from(b)

    if (aClone.toString() !== bClone.toString())
      return false

    let loopArrayFlag = true
    aClone.forEach((aCloneInstance, aCloneIndex) => {
      if (loopArrayFlag)
        if (
          aCloneInstance !== bClone[ aCloneIndex ] &&
          !equals(aCloneInstance, bClone[ aCloneIndex ])
        )
          loopArrayFlag = false

    })

    return loopArrayFlag
  }

  const aRegex = parseRegex(a)
  const bRegex = parseRegex(b)

  if (aRegex[ 0 ])
    return bRegex[ 0 ] ? aRegex[ 1 ] === bRegex[ 1 ] : false
  else if (bRegex[ 0 ]) return false

  const aDate = parseDate(a)
  const bDate = parseDate(b)

  if (aDate[ 0 ])
    return bDate[ 0 ] ? aDate[ 1 ] === bDate[ 1 ] : false
  else if (bDate[ 0 ]) return false

  if (a instanceof Error){
    if (!(b instanceof Error)) return false

    return compareErrors(a, b)
  }

  if (aType === 'Set')
    return _compareSets(a, b)

  if (aType === 'Object'){
    const aKeys = Object.keys(a)

    if (aKeys.length !== Object.keys(b).length)
      return false

    let loopObjectFlag = true
    aKeys.forEach(aKeyInstance => {
      if (loopObjectFlag){
        const aValue = a[ aKeyInstance ]
        const bValue = b[ aKeyInstance ]

        if (aValue !== bValue && !equals(aValue, bValue))
          loopObjectFlag = false

      }
    })

    return loopObjectFlag
  }

  return false
}

import { equals as equalsRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { variousTypes } from './benchmarks/_utils.js'
import { equals } from './equals.js'

test('compare functions', () => {
  function foo(){}
  function bar(){}
  const baz = () => {}

  const expectTrue = equals(foo, foo)
  const expectFalseFirst = equals(foo, bar)
  const expectFalseSecond = equals(foo, baz)

  expect(expectTrue).toBeTrue()
  expect(expectFalseFirst).toBeFalse()
  expect(expectFalseSecond).toBeFalse()
})

test('with array of objects', () => {
  const list1 = [ { a : 1 }, [ { b : 2 } ] ]
  const list2 = [ { a : 1 }, [ { b : 2 } ] ]
  const list3 = [ { a : 1 }, [ { b : 3 } ] ]

  expect(equals(list1, list2)).toBeTrue()
  expect(equals(list1, list3)).toBeFalse()
})

test('with regex', () => {
  expect(equals(/s/, /s/)).toBeTrue()
  expect(equals(/s/, /d/)).toBeFalse()
  expect(equals(/a/gi, /a/gi)).toBeTrue()
  expect(equals(/a/gim, /a/gim)).toBeTrue()
  expect(equals(/a/gi, /a/i)).toBeFalse()
})

test('not a number', () => {
  expect(equals([ NaN ], [ NaN ])).toBeTrue()
})

test('new number', () => {
  expect(equals(new Number(0), new Number(0))).toBeTrue()
  expect(equals(new Number(0), new Number(1))).toBeFalse()
  expect(equals(new Number(1), new Number(0))).toBeFalse()
})

test('new string', () => {
  expect(equals(new String(''), new String(''))).toBeTrue()
  expect(equals(new String(''), new String('x'))).toBeFalse()
  expect(equals(new String('x'), new String(''))).toBeFalse()
  expect(equals(new String('foo'), new String('foo'))).toBeTrue()
  expect(equals(new String('foo'), new String('bar'))).toBeFalse()
  expect(equals(new String('bar'), new String('foo'))).toBeFalse()
})

test('new Boolean', () => {
  expect(equals(new Boolean(true), new Boolean(true))).toBeTrue()
  expect(equals(new Boolean(false), new Boolean(false))).toBeTrue()
  expect(equals(new Boolean(true), new Boolean(false))).toBeFalse()
  expect(equals(new Boolean(false), new Boolean(true))).toBeFalse()
})

test('new Error', () => {
  expect(equals(new Error('XXX'), {})).toBeFalse()
  expect(equals(new Error('XXX'), new TypeError('XXX'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('YYY'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
  expect(equals(new Error('XXX'), new TypeError('YYY'))).toBeFalse()
  expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
})

test('with dates', () => {
  expect(equals(new Date(0), new Date(0))).toBeTrue()
  expect(equals(new Date(1), new Date(1))).toBeTrue()
  expect(equals(new Date(0), new Date(1))).toBeFalse()
  expect(equals(new Date(1), new Date(0))).toBeFalse()
  expect(equals(new Date(0), {})).toBeFalse()
  expect(equals({}, new Date(0))).toBeFalse()
})

test('ramda spec', () => {
  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toBeTrue()

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 2,
    b : 3,
  })).toBeTrue()

  expect(equals({
    a : 2,
    b : 3,
  },
  {
    a : 3,
    b : 3,
  })).toBeFalse()

  expect(equals({
    a : 2,
    b : 3,
    c : 1,
  },
  {
    a : 2,
    b : 3,
  })).toBeFalse()
})

test('works with boolean tuple', () => {
  expect(equals([ true, false ], [ true, false ])).toBeTrue()
  expect(equals([ true, false ], [ true, true ])).toBeFalse()
})

test('works with equal objects within array', () => {
  const objFirst = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }
  const objSecond = {
    a : {
      b : 1,
      c : 2,
      d : [ 1 ],
    },
  }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeTrue()
})

test('works with different objects within array', () => {
  const objFirst = { a : { b : 1 } }
  const objSecond = { a : { b : 2 } }

  const x = [ 1, 2, objFirst, null, '', [] ]
  const y = [ 1, 2, objSecond, null, '', [] ]
  expect(equals(x, y)).toBeFalse()
})

test('works with undefined as second argument', () => {
  expect(equals(1, undefined)).toBeFalse()

  expect(equals(undefined, undefined)).toBeTrue()
})

test('compare sets', () => {
  const toCompareDifferent = new Set([ { a : 1 }, { a : 2 } ])
  const toCompareSame = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
  const testSet = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
  expect(equals(toCompareSame, testSet)).toBeTruthy()
  expect(equals(toCompareDifferent, testSet)).toBeFalsy()
  expect(equalsRamda(toCompareSame, testSet)).toBeTruthy()
  expect(equalsRamda(toCompareDifferent, testSet)).toBeFalsy()
})

test('compare simple sets', () => {
  const testSet = new Set([ '2', '3', '3', '2', '1' ])
  expect(equals(new Set([ '3', '2', '1' ]), testSet)).toBeTruthy()
  expect(equals(new Set([ '3', '2', '0' ]), testSet)).toBeFalsy()
})

test('various examples', () => {
  expect(equals([ 1, 2, 3 ])([ 1, 2, 3 ])).toBeTrue()

  expect(equals([ 1, 2, 3 ], [ 1, 2 ])).toBeFalse()

  expect(equals(1, 1)).toBeTrue()

  expect(equals(1, '1')).toBeFalse()

  expect(equals({}, {})).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
  })).toBeTrue()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : false,
  },
  {
    a : 1,
    b : 1,
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 2,
    c : 3,
  })).toBeFalse()

  expect(equals({
    x : {
      a : 1,
      b : 2,
    },
  },
  {
    x : {
      a : 1,
      b : 2,
      c : 3,
    },
  })).toBeFalse()

  expect(equals({
    a : 1,
    b : 2,
  },
  {
    a : 1,
    b : 3,
  })).toBeFalse()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 1 } } })).toBeTrue()

  expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 2 } } })).toBeFalse()

  expect(equals({ a : {} }, { a : {} })).toBeTrue()

  expect(equals('', '')).toBeTrue()

  expect(equals('foo', 'foo')).toBeTrue()

  expect(equals('foo', 'bar')).toBeFalse()

  expect(equals(0, false)).toBeFalse()

  expect(equals(/\s/g, null)).toBeFalse()

  expect(equals(null, null)).toBeTrue()

  expect(equals(false)(null)).toBeFalse()
})

test('with custom functions', () => {
  function foo(){
    return 1
  }
  foo.prototype.toString = () => ''
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with classes', () => {
  class Foo{}
  const foo = new Foo()
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with negative zero', () => {
  expect(equals(-0, -0)).toBeTrue()
  expect(equals(-0, 0)).toBeFalse()
  expect(equals(0, 0)).toBeTrue()
  expect(equals(-0, 1)).toBeFalse()
})

test('with big int', () => {
  const a = BigInt(9007199254740991)
  const b = BigInt(9007199254740991)
  const c = BigInt(7007199254740991)
  expect(equals(a, b)).toBeTrue()
  expect(equals(a, c)).toBeFalse()
})

describe('brute force', () => {
  compareCombinations({
    callback : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
{
  "ERRORS_MESSAGE_MISMATCH": 0,
  "ERRORS_TYPE_MISMATCH": 0,
  "RESULTS_MISMATCH": 0,
  "SHOULD_NOT_THROW": 0,
  "SHOULD_THROW": 0,
  "TOTAL_TESTS": 289,
}
`)
    },
    firstInput  : variousTypes,
    fn          : equals,
    fnRamda     : equalsRamda,
    secondInput : variousTypes,
  })
})

evolve

evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[]

It takes object or array of functions as set of rules. These rules are applied to the iterable input to produce the result.

:boom: Error handling of this method differs between Ramda and Rambda. Ramda for some wrong inputs returns result and for other - it returns one of the inputs. Rambda simply throws when inputs are not correct. Full details for this mismatch are listed in source/_snapshots/evolve.spec.js.snap file.

const rules = {
  foo : add(1),
  bar : add(-1),
}
const input = {
  a   : 1,
  foo : 2,
  bar : 3,
}
const result = evolve(rules, input)
const expected = {
  a   : 1,
  foo : 3,
  bar : 2,
})
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20rules%20%3D%20%7B%0A%20%20foo%20%3A%20add(1)%2C%0A%20%20bar%20%3A%20add(-1)%2C%0A%7D%0Aconst%20input%20%3D%20%7B%0A%20%20a%20%20%20%3A%201%2C%0A%20%20foo%20%3A%202%2C%0A%20%20bar%20%3A%203%2C%0A%7D%0Aconst%20result%20%3D%20evolve(rules%2C%20input)%0Aconst%20expected%20%3D%20%7B%0A%20%20a%20%20%20%3A%201%2C%0A%20%20foo%20%3A%203%2C%0A%20%20bar%20%3A%202%2C%0A%7D)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.evolve</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { mapArray, mapObject } from './map.js'
import { type } from './type.js'

export function evolveArray(rules, list){
  return mapArray(
    (x, i) => {
      if (type(rules[ i ]) === 'Function'){
        return rules[ i ](x)
      }

      return x
    },
    list,
    true
  )
}

export function evolveObject(rules, iterable){
  return mapObject((x, prop) => {
    if (type(x) === 'Object'){
      const typeRule = type(rules[ prop ])
      if (typeRule === 'Function'){
        return rules[ prop ](x)
      }
      if (typeRule === 'Object'){
        return evolve(rules[ prop ], x)
      }

      return x
    }
    if (type(rules[ prop ]) === 'Function'){
      return rules[ prop ](x)
    }

    return x
  }, iterable)
}

export function evolve(rules, iterable){
  if (arguments.length === 1){
    return _iterable => evolve(rules, _iterable)
  }
  const rulesType = type(rules)
  const iterableType = type(iterable)

  if (iterableType !== rulesType){
    throw new Error('iterableType !== rulesType')
  }

  if (![ 'Object', 'Array' ].includes(rulesType)){
    throw new Error(`'iterable' and 'rules' are from wrong type ${ rulesType }`)
  }

  if (iterableType === 'Object'){
    return evolveObject(rules, iterable)
  }

  return evolveArray(rules, iterable)
}

import { evolve as evolveRamda } from 'ramda'

import { add } from '../rambda.js'
import { compareCombinations, compareToRamda } from './_internals/testUtils.js'
import { evolve } from './evolve.js'

test('happy', () => {
  const rules = {
    foo    : add(1),
    nested : { bar : x => Object.keys(x).length },
  }
  const input = {
    a      : 1,
    foo    : 2,
    nested : { bar : { z : 3 } },
  }
  const result = evolve(rules, input)
  expect(result).toEqual({
    a      : 1,
    foo    : 3,
    nested : { bar : 1 },
  })
})

test('nested rule is wrong', () => {
  const rules = {
    foo    : add(1),
    nested : { bar : 10 },
  }
  const input = {
    a      : 1,
    foo    : 2,
    nested : { bar : { z : 3 } },
  }
  const result = evolve(rules)(input)
  expect(result).toEqual({
    a      : 1,
    foo    : 3,
    nested : { bar : { z : 3 } },
  })
})

test('is recursive', () => {
  const rules = {
    nested : {
      second : add(-1),
      third  : add(1),
    },
  }
  const object = {
    first  : 1,
    nested : {
      second : 2,
      third  : 3,
    },
  }
  const expected = {
    first  : 1,
    nested : {
      second : 1,
      third  : 4,
    },
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('ignores primitive values', () => {
  const rules = {
    n : 2,
    m : 'foo',
  }
  const object = {
    n : 0,
    m : 1,
  }
  const expected = {
    n : 0,
    m : 1,
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('with array', () => {
  const rules = [ add(1), add(-1) ]
  const list = [ 100, 1400 ]
  const expected = [ 101, 1399 ]
  const result = evolve(rules, list)
  expect(result).toEqual(expected)
})

const rulesObject = { a : add(1) }
const rulesList = [ add(1) ]
const possibleIterables = [ null, undefined, '', 42, [], [ 1 ], { a : 1 } ]
const possibleRules = [ ...possibleIterables, rulesList, rulesObject ]

describe('brute force', () => {
  compareCombinations({
    firstInput : possibleRules,
    callback   : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 4,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 63,
        }
      `)
    },
    secondInput : possibleIterables,
    fn          : evolve,
    fnRamda     : evolveRamda,
  })
})

excludes

Opposite of R.includes

R.equals is used to determine equality.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.excludes('ar'%2C%20'foo')%2C%0A%20%20R.excludes(%7Ba%3A%202%7D%2C%20%5B%7Ba%3A%201%7D%5D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%20%5D">Try this <strong>R.excludes</strong> example in Rambda REPL</a>

F

F(): boolean

F() // => false

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20F()%20%2F%2F%20%3D%3E%20false">Try this <strong>R.F</strong> example in Rambda REPL</a>

export function F(){
  return false
}

filter

filter<T>(predicate: Predicate<T>): (input: T[]) => T[]

It filters list or object input using a predicate function.

const list = [3, 4, 3, 2]
const listPredicate = x => x > 2

const object = {abc: 'fo', xyz: 'bar', baz: 'foo'}
const objectPredicate = (x, prop) => x.length + prop.length > 5

const result = [
  R.filter(listPredicate, list),
  R.filter(objectPredicate, object)
]
// => [ [3, 4], { xyz: 'bar', baz: 'foo'} ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B3%2C%204%2C%203%2C%202%5D%0Aconst%20listPredicate%20%3D%20x%20%3D%3E%20x%20%3E%202%0A%0Aconst%20object%20%3D%20%7Babc%3A%20'fo'%2C%20xyz%3A%20'bar'%2C%20baz%3A%20'foo'%7D%0Aconst%20objectPredicate%20%3D%20(x%2C%20prop)%20%3D%3E%20x.length%20%2B%20prop.length%20%3E%205%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.filter(listPredicate%2C%20list)%2C%0A%20%20R.filter(objectPredicate%2C%20object)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%20%5B3%2C%204%5D%2C%20%7B%20xyz%3A%20'bar'%2C%20baz%3A%20'foo'%7D%20%5D">Try this <strong>R.filter</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

export function filterObject(predicate, obj){
  const willReturn = {}

  for (const prop in obj){
    if (predicate(
      obj[ prop ], prop, obj
    )){
      willReturn[ prop ] = obj[ prop ]
    }
  }

  return willReturn
}

export function filterArray(
  predicate, list, indexed = false
){
  let index = 0
  const len = list.length
  const willReturn = []

  while (index < len){
    const predicateResult = indexed ?
      predicate(list[ index ], index) :
      predicate(list[ index ])
    if (predicateResult){
      willReturn.push(list[ index ])
    }

    index++
  }

  return willReturn
}

export function filter(predicate, iterable){
  if (arguments.length === 1)
    return _iterable => filter(predicate, _iterable)
  if (!iterable){
    throw new Error('Incorrect iterable input')
  }

  if (isArray(iterable)) return filterArray(
    predicate, iterable, false
  )

  return filterObject(predicate, iterable)
}

import { filter as filterRamda } from 'ramda'

import { filter } from './filter.js'
import { T } from './T.js'

const sampleObject = {
  a : 1,
  b : 2,
  c : 3,
  d : 4,
}

test('happy', () => {
  const isEven = n => n % 2 === 0

  expect(filter(isEven, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
  expect(filter(isEven, {
    a : 1,
    b : 2,
    d : 3,
  })).toEqual({ b : 2 })
})

test('predicate when input is object', () => {
  const obj = {
    a : 1,
    b : 2,
  }
  const predicate = (
    val, prop, inputObject
  ) => {
    expect(inputObject).toEqual(obj)
    expect(typeof prop).toBe('string')

    return val < 2
  }
  expect(filter(predicate, obj)).toEqual({ a : 1 })
})

test('with object', () => {
  const isEven = n => n % 2 === 0
  const result = filter(isEven, sampleObject)
  const expectedResult = {
    b : 2,
    d : 4,
  }

  expect(result).toEqual(expectedResult)
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(() => filter(T, null)).toThrowWithMessage(Error,
    'Incorrect iterable input')
  expect(() => filter(T)(undefined)).toThrowWithMessage(Error,
    'Incorrect iterable input')
  expect(() => filterRamda(T, null)).toThrowWithMessage(TypeError,
    'Cannot read properties of null (reading \'fantasy-land/filter\')')
  expect(() => filterRamda(T, undefined)).toThrowWithMessage(TypeError,
    'Cannot read properties of undefined (reading \'fantasy-land/filter\')')
})

filterArray

filterArray<T>(predicate: Predicate<T>): (input: T[]) => T[]

const result = R.filterArray(
  x => x > 1,
  [1, 2, 3]
)
// => [1, 3]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.filterArray(%0A%20%20x%20%3D%3E%20x%20%3E%201%2C%0A%20%20%5B1%2C%202%2C%203%5D%0A)%0A%2F%2F%20%3D%3E%20%5B1%2C%203%5D">Try this <strong>R.filterArray</strong> example in Rambda REPL</a>

filterAsync

filterAsync<T>(fn: AsyncPredicate<T>, list: T[]): Promise<T[]>

Asynchronous version of R.filter

const predicate = async x => {
  await R.delay(100)
  return x % 2 === 1
}
const result = await R.filterAsync(predicate, [ 1, 2, 3 ])
// => [ 1, 3 ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20%25%202%20%3D%3D%3D%201%0A%7D%0Aconst%20result%20%3D%20await%20R.filterAsync(predicate%2C%20%5B%201%2C%202%2C%203%20%5D)%0A%2F%2F%20%3D%3E%20%5B%201%2C%203%20%5D">Try this <strong>R.filterAsync</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { filter } from './filter.js'
import { mapAsync } from './mapAsync.js'

export function filterAsyncFn(predicate, listOrObject){
  return new Promise((resolve, reject) => {
    mapAsync(predicate, listOrObject)
      .then(predicateResult => {
        if (isArray(predicateResult)){
          const filtered = listOrObject.filter((_, i) => predicateResult[ i ])

          return resolve(filtered)
        }
        const filtered = filter((_, prop) => predicateResult[ prop ],
          listOrObject)

        return resolve(filtered)
      })
      .catch(reject)
  })
}

export function filterAsync(predicate, listOrObject){
  if (arguments.length === 1){
    return async _listOrObject => filterAsyncFn(predicate, _listOrObject)
  }

  return new Promise((resolve, reject) => {
    filterAsyncFn(predicate, listOrObject).then(resolve)
      .catch(reject)
  })
}

import { delay } from './delay.js'
import { filterAsync } from './filterAsync.js'

test('happy', async () => {
  const predicate = async (x, i) => {
    expect(i).toBeNumber()
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate)([ 1, 2, 3 ])
  expect(result).toEqual([ 1, 3 ])
})

test('with object', async () => {
  const predicate = async (x, prop) => {
    expect(prop).toBeString()
    await delay(100)

    return x % 2 === 1
  }
  const result = await filterAsync(predicate, {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
    e : 5,
  })

  expect(result).toEqual({
    a : 1,
    c : 3,
    e : 5,
  })
})

filterIndexed

Same as R.filter, but it passes index/property as second argument to the predicate, when looping over arrays/objects.

filterObject

filterObject<T>(predicate: ObjectPredicate<T>): (x: Dictionary<T>) => Dictionary<T>

const obj = {a: 1, b:2}
const result = R.filterObject(
  x => x > 1,
  obj
)
// => {b: 2}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A2%7D%0Aconst%20result%20%3D%20R.filterObject(%0A%20%20x%20%3D%3E%20x%20%3E%201%2C%0A%20%20obj%0A)%0A%2F%2F%20%3D%3E%20%7Bb%3A%202%7D">Try this <strong>R.filterObject</strong> example in Rambda REPL</a>

find

find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined

It returns the first element of list that satisfy the predicate.

If there is no such element, it returns undefined.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.find(predicate, list)
// => {foo: 1}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%20'bar'%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.find(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%7Bfoo%3A%201%7D">Try this <strong>R.find</strong> example in Rambda REPL</a>

export function find(predicate, list){
  if (arguments.length === 1) return _list => find(predicate, _list)

  let index = 0
  const len = list.length

  while (index < len){
    const x = list[ index ]
    if (predicate(x)){
      return x
    }

    index++
  }
}

import { find } from './find.js'
import { propEq } from './propEq.js'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  const fn = propEq(2, 'a')
  expect(find(fn, list)).toEqual({ a : 2 })
})

test('with curry', () => {
  const fn = propEq(4, 'a')
  expect(find(fn)(list)).toBeUndefined()
})

test('with empty list', () => {
  expect(find(() => true, [])).toBeUndefined()
})

findAsync

Asynchronous version of R.find.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0A%7D%0A%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%20'bar'%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20await%20R.findAsync(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%7Bfoo%3A%201%7D">Try this <strong>R.findAsync</strong> example in Rambda REPL</a>

findIndex

findIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the first element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.findIndex(predicate, list)
// => 1

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%20'bar'%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.findIndex(predicate%2C%20list)%0A%2F%2F%20%3D%3E%201">Try this <strong>R.findIndex</strong> example in Rambda REPL</a>

export function findIndex(predicate, list){
  if (arguments.length === 1) return _list => findIndex(predicate, _list)

  const len = list.length
  let index = -1

  while (++index < len){
    if (predicate(list[ index ])){
      return index
    }
  }

  return -1
}

import { findIndex } from './findIndex.js'
import { propEq } from './propEq.js'

const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]

test('happy', () => {
  expect(findIndex(propEq(2, 'a'), list)).toBe(1)
  expect(findIndex(propEq(1, 'a'))(list)).toBe(0)
  expect(findIndex(propEq(4, 'a'))(list)).toBe(-1)
})

findLast

findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined

It returns the last element of list satisfying the predicate function.

If there is no such element, then undefined is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLast(predicate, list)
// => {foo: 1}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%200%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.findLast(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%7Bfoo%3A%201%7D">Try this <strong>R.findLast</strong> example in Rambda REPL</a>

export function findLast(predicate, list){
  if (arguments.length === 1) return _list => findLast(predicate, _list)

  let index = list.length

  while (--index >= 0){
    if (predicate(list[ index ])){
      return list[ index ]
    }
  }

  return undefined
}

import { findLast } from './findLast.js'

test('happy', () => {
  const result = findLast(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])
  expect(result).toBe(4)

  expect(findLast(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})

test('with curry', () => {
  expect(findLast(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(4)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLast(even, a)).toBe(0)
  expect(findLast(gt100, a)).toBe(300)
  expect(findLast(isStr, a)).toBe('cow')
  expect(findLast(xGt100, a)).toEqual(obj2)
})

test('ramda 2', () => {
  expect(findLast(even, [ 'zing' ])).toBeUndefined()
})

test('ramda 3', () => {
  expect(findLast(even, [ 2, 3, 5 ])).toBe(2)
})

test('ramda 4', () => {
  expect(findLast(even, [])).toBeUndefined()
})

findLastIndex

findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the last element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLastIndex(predicate, list)
// => 1

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%200%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.findLastIndex(predicate%2C%20list)%0A%2F%2F%20%3D%3E%201">Try this <strong>R.findLastIndex</strong> example in Rambda REPL</a>

export function findLastIndex(fn, list){
  if (arguments.length === 1) return _list => findLastIndex(fn, _list)

  let index = list.length

  while (--index >= 0){
    if (fn(list[ index ])){
      return index
    }
  }

  return -1
}

import { findLastIndex } from './findLastIndex.js'

test('happy', () => {
  const result = findLastIndex(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])

  expect(result).toBe(5)

  expect(findLastIndex(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})

test('with curry', () => {
  expect(findLastIndex(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(5)
})

const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
  return x % 2 === 0
}
const gt100 = function (x){
  return x > 100
}
const isStr = function (x){
  return typeof x === 'string'
}
const xGt100 = function (o){
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLastIndex(even, a)).toBe(15)
  expect(findLastIndex(gt100, a)).toBe(9)
  expect(findLastIndex(isStr, a)).toBe(3)
  expect(findLastIndex(xGt100, a)).toBe(10)
})

test('ramda 2', () => {
  expect(findLastIndex(even, [ 'zing' ])).toBe(-1)
})

test('ramda 3', () => {
  expect(findLastIndex(even, [ 2, 3, 5 ])).toBe(0)
})

test('ramda 4', () => {
  expect(findLastIndex(even, [])).toBe(-1)
})

flatten

flatten<T>(list: any[]): T[]

It deeply flattens an array.

const result = R.flatten([
  1, 
  2, 
  [3, 30, [300]], 
  [4]
])
// => [ 1, 2, 3, 30, 300, 4 ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.flatten(%5B%0A%20%201%2C%20%0A%20%202%2C%20%0A%20%20%5B3%2C%2030%2C%20%5B300%5D%5D%2C%20%0A%20%20%5B4%5D%0A%5D)%0A%2F%2F%20%3D%3E%20%5B%201%2C%202%2C%203%2C%2030%2C%20300%2C%204%20%5D">Try this <strong>R.flatten</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

export function flatten(list, input){
  const willReturn = input === undefined ? [] : input

  for (let i = 0; i < list.length; i++){
    if (isArray(list[ i ])){
      flatten(list[ i ], willReturn)
    } else {
      willReturn.push(list[ i ])
    }
  }

  return willReturn
}

import { flatten } from './flatten.js'

test('happy', () => {
  expect(flatten([ 1, 2, 3, [ [ [ [ [ 4 ] ] ] ] ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ 3 ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, [ 2, [ [ [ 3 ] ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])

  expect(flatten([ 1, 2, [ 3, 4 ], 5, [ 6, [ 7, 8, [ 9, [ 10, 11 ], 12 ] ] ] ])).toEqual([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ])
})

test('readme example', () => {
  const result = flatten([ 1, 2, [ 3, 30, [ 300 ] ], [ 4 ] ])
  expect(result).toEqual([ 1, 2, 3, 30, 300, 4 ])
})

flip

It returns function which calls fn with exchanged first and second argument.

:boom: Rambda's flip will throw if the arity of the input function is greater or equal to 5.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20subtractFlip%20%3D%20R.flip(R.subtract)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20subtractFlip(1%2C7)%2C%0A%20%20R.subtract(1%2C%206)%0A%5D%20%20%0A%2F%2F%20%3D%3E%20%5B6%2C%20-6%5D">Try this <strong>R.flip</strong> example in Rambda REPL</a>

forEach

forEach<T>(fn: Iterator<T, void>, list: T[]): T[]

It applies iterable function over all members of list and returns list.

:boom: It works with objects, unlike Ramda.

const sideEffect = {}
const result = R.forEach(
  x => sideEffect[`foo${x}`] = x
)([1, 2])

sideEffect // => {foo1: 1, foo2: 2}
result // => [1, 2]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20sideEffect%20%3D%20%7B%7D%0Aconst%20result%20%3D%20R.forEach(%0A%20%20x%20%3D%3E%20sideEffect%5B%60foo%24%7Bx%7D%60%5D%20%3D%20x%0A)(%5B1%2C%202%5D)%0A%0AsideEffect%20%2F%2F%20%3D%3E%20%7Bfoo1%3A%201%2C%20foo2%3A%202%7D%0Aresult%20%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.forEach</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { forEachObjIndexedFn } from './forEachObjIndexed.js'

export function forEach(fn, iterable){
  if (arguments.length === 1) return _list => forEach(fn, _list)
  if (iterable === undefined) return

  if (isArray(iterable)){
    let index = 0
    const len = iterable.length

    while (index < len){
      fn(iterable[ index ])
      index++
    }
  } else return forEachObjIndexedFn(fn, iterable)

  return iterable
}

import { forEach } from './forEach.js'
import { type } from './type.js'

test('happy', () => {
  const sideEffect = {}
  forEach(x => sideEffect[ `foo${ x }` ] = x + 10)([ 1, 2 ])

  expect(sideEffect).toEqual({
    foo1 : 11,
    foo2 : 12,
  })
})

test('iterate over object', () => {
  const obj = {
    a : 1,
    b : [ 1, 2 ],
    c : { d : 7 },
    f : 'foo',
  }
  const result = {}
  const returned = forEach((
    val, prop, inputObj
  ) => {
    expect(type(inputObj)).toBe('Object')
    result[ prop ] = `${ prop }-${ type(val) }`
  })(obj)

  const expected = {
    a : 'a-Number',
    b : 'b-Array',
    c : 'c-Object',
    f : 'f-String',
  }

  expect(result).toEqual(expected)
  expect(returned).toEqual(obj)
})

test('with empty list', () => {
  const list = []
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('with wrong input', () => {
  const list = undefined
  const result = forEach(x => x * x)(list)

  expect(result).toBeUndefined()
})

test('returns the input', () => {
  const list = [ 1, 2, 3 ]
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

forEachIndexed

forEachObjIndexed

fromPairs

It transforms a listOfPairs to an object.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20listOfPairs%20%3D%20%5B%20%5B%20'a'%2C%201%20%5D%2C%20%5B%20'b'%2C%202%20%5D%2C%20%5B%20'c'%2C%20%5B%203%2C%204%20%5D%20%5D%20%5D%0Aconst%20expected%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%202%2C%0A%20%20c%20%3A%20%5B%203%2C%204%20%5D%2C%0A%7D%0A%0Aconst%20result%20%3D%20R.fromPairs(listOfPairs)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.fromPairs</strong> example in Rambda REPL</a>

getter

getter<T>(keyOrKeys: string | string[] | undefined): T

The set of methods R.setter, R.getter and R.reset allow different parts of your logic to access communicate indirectly via shared cache object.

Usually these methods show that you might need to refactor to classes. Still, they can be helpful meanwhile.

R.getter: It provides access to the cache object. If undefined is used as a key, this method will return the whole cache object. If string is passed, then it will return cache value for this key. If array of string is passed, then it assume that this is array of keys and it will return the corresponding cache values for these keys.

R.setter: It allows cache object's keys to be changed. You can either set individual key-value pairs with R.setter(key, value) or you pass directly object, which will be merged with the cache object.

R.reset: It resets the cache object.

R.setter('foo','bar')
R.setter('a', 1)
R.getter(['foo','a']) // => {foo: 'bar', a: 1}

R.setter('a', 2)
R.getter('a') // => 2
R.reset()
R.getter('a') // => undefined

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.setter('foo'%2C'bar')%0AR.setter('a'%2C%201)%0AR.getter(%5B'foo'%2C'a'%5D)%20%2F%2F%20%3D%3E%20%7Bfoo%3A%20'bar'%2C%20a%3A%201%7D%0A%0AR.setter('a'%2C%202)%0AR.getter('a')%20%2F%2F%20%3D%3E%202%0AR.reset()%0Aconst%20result%20%3D%20R.getter('a')%20%2F%2F%20%3D%3E%20undefined">Try this <strong>R.getter</strong> example in Rambda REPL</a>

import { mergeRight } from './mergeRight.js'
import { pick } from './pick.js'
import { type } from './type.js'

let holder = {}

/**
 * Pass string to get value
 * Pass array to get object of values
 * Pass undefined to get all data
 */
export function getter(key){
  const typeKey = type(key)

  if (typeKey === 'String') return holder[ key ]

  if (typeKey === 'Array') return pick(key, holder)

  return holder
}

export function setter(maybeKey, maybeValue){
  const typeKey = type(maybeKey)
  const typeValue = type(maybeValue)

  if (typeKey === 'String'){
    if (typeValue === 'Function'){
      return holder[ maybeKey ] = maybeValue(holder[ maybeKey ])
    }

    return holder[ maybeKey ] = maybeValue
  }

  if (typeKey !== 'Object') return

  holder = mergeRight(holder, maybeKey)
}

export function reset(){
  holder = {}
}

import { add } from './add.js'
import { getter, reset, setter } from './getter.js'

afterEach(() => {
  reset()
})

test('happy', () => {
  const key = 'foo'
  setter(key, 1)

  expect(getter(key)).toBe(1)
})

test('docs example', () => {
  setter('foo', 'bar')
  setter('a', 1)
  expect(getter([ 'foo', 'a' ])).toEqual({
    foo : 'bar',
    a   : 1,
  })

  setter('a', 2)
  expect(getter('a')).toBe(2)
  reset()
  expect(getter('a')).toBeUndefined()
})

test('when array is key in getter', () => {
  setter({
    a : 1,
    b : 2,
    c : 3,
  })

  expect(getter([ 'a', 'b' ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('getter with undefined as key returns all', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)

  expect(getter()).toEqual(data)
})

test('function as setter value', () => {
  const data = {
    a : 1,
    b : 2,
    c : 3,
  }

  setter(data)
  setter('a', add(10))

  expect(getter()).toEqual({
    a : 11,
    b : 2,
    c : 3,
  })
})

test('setter fallbacks to undefined', () => {
  expect(setter()).toBeUndefined
})

glue

glue(input: string, glueString?: string): string

It transforms multiline string to single line by gluing together the separate lines with the glueString and removing the empty spaces. By default glueString is equal to single space, so if that is what you need, then you can just pass a single argument.

const result = R.glue(`
  foo
  bar
  baz
`)
// => 'foo bar baz'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.glue(%60%0A%20%20foo%0A%20%20bar%0A%20%20baz%0A%60)%0A%2F%2F%20%3D%3E%20'foo%20bar%20baz'">Try this <strong>R.glue</strong> example in Rambda REPL</a>

export function glue(input, glueChar){
  return input
    .split('\n')
    .filter(x => x.trim().length > 0)
    .map(x => x.trim())
    .join(glueChar === undefined ? ' ' : glueChar)
}

import { glue } from './glue.js'

test('empty string as a glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '')

  const expectedResult = 'foobarbaz'

  expect(result).toBe(expectedResult)
})

test('case 0', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = false
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 1', () => {
  const zero = 'node node_modules/jest'
  const first = '--runInBand'
  const last = '-- src/a.spec.js'
  const flag = true
  const result = glue(`
    ${ zero }
    ${ first }
    ${ flag ? '--env=node' : '' }
    ${ last }
  `)

  const expectedResult = `${ zero } ${ first } --env=node ${ last }`

  expect(result).toBe(expectedResult)
})

test('case 2', () => {
  const first = '--runInBand'
  const result = glue(`
    zero
    ${ first }
    last
  `)
  const expectedResult = `zero ${ first } last`

  expect(result).toBe(expectedResult)
})

test('case 3', () => {
  const result = glue(`
    foo
    bar
    baz
  `)

  const expectedResult = 'foo bar baz'

  expect(result).toBe(expectedResult)
})

test('with glue', () => {
  const result = glue(`
    foo
    bar
    baz
  `,
  '==')

  const expectedResult = 'foo==bar==baz'

  expect(result).toBe(expectedResult)
})

groupBy

It splits list according to a provided groupFn function and returns an object.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%20'a'%2C%20'b'%2C%20'aa'%2C%20'bb'%20%5D%0Aconst%20groupFn%20%3D%20x%20%3D%3E%20x.length%0A%0Aconst%20result%20%3D%20R.groupBy(groupFn%2C%20list)%0A%2F%2F%20%3D%3E%20%7B%20'1'%3A%20%5B'a'%2C%20'b'%5D%2C%20'2'%3A%20%5B'aa'%2C%20'bb'%5D%20%7D">Try this <strong>R.groupBy</strong> example in Rambda REPL</a>

groupWith

It returns separated version of list or string input, where separation is done with equality compareFn function.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20isConsecutive%20%3D%20(x%2C%20y)%20%3D%3E%20x%20%3D%3D%3D%20y%0Aconst%20list%20%3D%20%5B1%2C%202%2C%202%2C%201%2C%201%2C%202%5D%0A%0Aconst%20result%20%3D%20R.groupWith(isConsecutive%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%5B1%5D%2C%20%5B2%2C2%5D%2C%20%5B1%2C1%5D%2C%20%5B2%5D%5D">Try this <strong>R.groupWith</strong> example in Rambda REPL</a>

gt

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.gt(2%2C%201)%2C%20R.gt(2%2C%203)%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.gt</strong> example in Rambda REPL</a>

gte

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.gte(2%2C%201)%2C%20R.gte(2%2C%202)%2C%20R.gte(2%2C%203)%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.gte</strong> example in Rambda REPL</a>

has

has<T>(prop: string, obj: T): boolean

It returns true if obj has property prop.

const obj = {a: 1}

const result = [
  R.has('a', Record<string, unknown>),
  R.has('b', Record<string, unknown>)
]
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.has('a'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.has('b'%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.has</strong> example in Rambda REPL</a>

export function has(prop, obj){
  if (arguments.length === 1) return _obj => has(prop, _obj)

  if (!obj) return false

  return obj.hasOwnProperty(prop)
}

import { has } from './has.js'

test('happy', () => {
  expect(has('a')({ a : 1 })).toBeTrue()
  expect(has('b', { a : 1 })).toBeFalse()
})

test('with non-object', () => {
  expect(has('a', undefined)).toBeFalse()
  expect(has('a', null)).toBeFalse()
  expect(has('a', true)).toBeFalse()
  expect(has('a', '')).toBeFalse()
  expect(has('a', /a/)).toBeFalse()
})

hasIn

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.hasIn('a'%2C%20%7Ba%3A%201%7D)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.hasIn</strong> example in Rambda REPL</a>

hasPath

hasPath<T>(
  path: string | string[],
  input: object
): boolean

It will return true, if input object has truthy path(calculated with R.path).

const path = 'a.b'
const pathAsArray = ['a', 'b']
const obj = {a: {b: []}}

const result = [
  R.hasPath(path, Record<string, unknown>),
  R.hasPath(pathAsArray, Record<string, unknown>),
  R.hasPath('a.c', Record<string, unknown>),
]
// => [true, true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20path%20%3D%20'a.b'%0Aconst%20pathAsArray%20%3D%20%5B'a'%2C%20'b'%5D%0Aconst%20obj%20%3D%20%7Ba%3A%20%7Bb%3A%20%5B%5D%7D%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.hasPath(path%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.hasPath(pathAsArray%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.hasPath('a.c'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.hasPath</strong> example in Rambda REPL</a>

import { path } from './path.js'

export function hasPath(pathInput, obj){
  if (arguments.length === 1){
    return objHolder => hasPath(pathInput, objHolder)
  }

  return path(pathInput, obj) !== undefined
}

import { hasPath } from './hasPath.js'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : [] } }

  const result = hasPath(path)(obj)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const path = 'a.b'
  const obj = {}

  const result = hasPath(path, obj)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

head

head(str: string): string

It returns the first element of list or string input. It returns undefined if array has length of 0.

const result = [
  R.head([1, 2, 3]),
  R.head('foo') 
]
// => [1, 'f']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.head(%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.head('foo')%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%20'f'%5D">Try this <strong>R.head</strong> example in Rambda REPL</a>

export function head(listOrString){
  if (typeof listOrString === 'string') return listOrString[ 0 ] || ''

  return listOrString[ 0 ]
}

import { head } from './head.js'

test('head', () => {
  expect(head([ 'fi', 'fo', 'fum' ])).toBe('fi')
  expect(head([])).toBeUndefined()
  expect(head('foo')).toBe('f')
  expect(head('')).toBe('')
})

identical

It returns true if its arguments a and b are identical.

Otherwise, it returns false.

:boom: Values are identical if they reference the same memory. NaN is identical to NaN; 0 and -0 are not identical.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20objA%20%3D%20%7Ba%3A%201%7D%3B%0Aconst%20objB%20%3D%20%7Ba%3A%201%7D%3B%0AR.identical(objA%2C%20objA)%3B%20%2F%2F%20%3D%3E%20true%0AR.identical(objA%2C%20objB)%3B%20%2F%2F%20%3D%3E%20false%0AR.identical(1%2C%201)%3B%20%2F%2F%20%3D%3E%20true%0AR.identical(1%2C%20'1')%3B%20%2F%2F%20%3D%3E%20false%0AR.identical(%5B%5D%2C%20%5B%5D)%3B%20%2F%2F%20%3D%3E%20false%0AR.identical(0%2C%20-0)%3B%20%2F%2F%20%3D%3E%20false%0Aconst%20result%20%3D%20R.identical(NaN%2C%20NaN)%3B%20%2F%2F%20%3D%3E%20true">Try this <strong>R.identical</strong> example in Rambda REPL</a>

identity

identity<T>(input: T): T

It just passes back the supplied input argument.

:boom: Logic

R.identity(7) // => 7

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.identity(7)%20%2F%2F%20%3D%3E%207">Try this <strong>R.identity</strong> example in Rambda REPL</a>

export function identity(x){
  return x
}

import { identity } from './identity.js'

test('happy', () => {
  expect(identity(7)).toBe(7)
  expect(identity(true)).toBeTrue()
  expect(identity({ a : 1 })).toEqual({ a : 1 })
})

ifElse

ifElse<T, TFiltered extends T, TOnTrueResult, TOnFalseResult>(
  pred: (a: T) => a is TFiltered,
  onTrue: (a: TFiltered) => TOnTrueResult,
  onFalse: (a: Exclude<T, TFiltered>) => TOnFalseResult,
): (a: T) => TOnTrueResult | TOnFalseResult

It expects condition, onTrue and onFalse functions as inputs and it returns a new function with example name of fn.

When fn`` is called with inputargument, it will return eitheronTrue(input)oronFalse(input)depending oncondition(input)` evaluation.

const fn = R.ifElse(
 x => x>10,
 x => x*2,
 x => x*10
)

const result = [ fn(8), fn(18) ]
// => [80, 36]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.ifElse(%0A%20x%20%3D%3E%20x%3E10%2C%0A%20x%20%3D%3E%20x*2%2C%0A%20x%20%3D%3E%20x*10%0A)%0A%0Aconst%20result%20%3D%20%5B%20fn(8)%2C%20fn(18)%20%5D%0A%2F%2F%20%3D%3E%20%5B80%2C%2036%5D">Try this <strong>R.ifElse</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

function ifElseFn(
  condition, onTrue, onFalse
){
  return (...input) => {
		const conditionResult =
      typeof condition === 'boolean' ? condition : condition(...input)
    if (Boolean(conditionResult) ){
      return onTrue(...input)
    }

    return onFalse(...input)
  }
}

export const ifElse = curry(ifElseFn)

import { always } from './always.js'
import { has } from './has.js'
import { identity } from './identity.js'
import { ifElse } from './ifElse.js'
import { prop } from './prop.js'
import * as R from 'ramda'

const condition = has('foo')
const v = function (a){
  return typeof a === 'number'
}
const t = function (a){
  return a + 1
}
const ifFn = x => prop('foo', x).length
const elseFn = () => false

test('happy', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('ramda spec', () => {
  const ifIsNumber = ifElse(v)
  expect(ifIsNumber(t, identity)(15)).toBe(16)
  expect(ifIsNumber(t, identity)('hello')).toBe('hello')
})

test('pass all arguments', () => {
  const identity = function (a){
    return a
  }
  const v = function (){
    return true
  }
  const onTrue = function (a, b){
    expect(a).toBe(123)
    expect(b).toBe('abc')
  }
  ifElse(
    v, onTrue, identity
  )(123, 'abc')
})

test('accept constant as condition', () => {
  const fn = ifElse(true)(always(true))(always(false))

  expect(fn()).toBeTrue()
})

test('accept constant as condition - case 2', () => {
  const fn = ifElse(
    false, always(true), always(false)
  )

  expect(fn()).toBeFalse()
})

test('curry 1', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('curry 2', () => {
  const fn = ifElse(condition)(ifFn)(elseFn)

  expect(fn({ foo : 'bar' })).toBe(3)
  expect(fn({ fo : 'bar' })).toBeFalse()
})

test('simple arity of 1', () => {
  const condition = x => x > 5
  const onTrue = x => x + 1
  const onFalse = x => x + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1)
  expect(result).toBe(11)
})

test('simple arity of 2', () => {
  const condition = (x, y) => x + y > 5
  const onTrue = (x, y) => x + y + 1
  const onFalse = (x, y) => x + y + 10
  const result = ifElse(
    condition, onTrue, onFalse
  )(1, 10)
  expect(result).toBe(12)
})

test('bug 750', () => {
	const value = 34;

	let result = ifElse(
	R.identity,
	R.always('true'),
	R.always('false')
	)(value)
	expect(result).toBe('true')
})

ifElseAsync

ifElseAsync<T, U>(
  condition: (x: T) => Promise<boolean>, 
  onTrue: (x: T) => U, 
  onFalse: (x: T) => U, 
  ): (x: T) => Promise<U>

Asynchronous version of R.ifElse. Any of condition, ifFn and elseFn can be either asynchronous or synchronous function.

const condition = async x => {
  await R.delay(100)
  return x > 1
}
const ifFn = async x => {
  await R.delay(100)
  return x + 1
}
const elseFn = async x => {
  await R.delay(100)
  return x - 1
}

const result = await R.ifElseAsync(
  condition,
  ifFn,
  elseFn  
)(1)
// => 0

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20condition%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20%3E%201%0A%7D%0Aconst%20ifFn%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20%2B%201%0A%7D%0Aconst%20elseFn%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20-%201%0A%7D%0A%0Aconst%20result%20%3D%20await%20R.ifElseAsync(%0A%20%20condition%2C%0A%20%20ifFn%2C%0A%20%20elseFn%20%20%0A)(1)%0A%2F%2F%20%3D%3E%200">Try this <strong>R.ifElseAsync</strong> example in Rambda REPL</a>

function createThenable(fn){
  return async function (...input){
    return fn(...input)
  }
}

export function ifElseAsync(
  condition, ifFn, elseFn
){
  return (...inputs) =>
    new Promise((resolve, reject) => {
      const conditionPromise = createThenable(condition)
      const ifFnPromise = createThenable(ifFn)
      const elseFnPromise = createThenable(elseFn)

      conditionPromise(...inputs)
        .then(conditionResult => {
          const promised =
            conditionResult === true ? ifFnPromise : elseFnPromise

          promised(...inputs)
            .then(resolve)
            .catch(reject)
        })
        .catch(reject)
    })
}

import { delay } from './delay.js'
import { ifElseAsync } from './ifElseAsync.js'

test('arity of 1 - condition is async', async () => {
  const condition = async x => {
    await delay(100)

    return x > 4
  }
  const whenTrue = x => x + 1
  const whenFalse = x => x + 10
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 1 - condition is sync', async () => {
  const condition = x => x > 4
  const whenTrue = async x => {
    await delay(100)

    return x + 1
  }
  const whenFalse = async x => {
    await delay(100)

    return x + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 1 - all inputs are async', async () => {
  const condition = async x => {
    await delay(100)

    return x > 4
  }
  const whenTrue = async x => {
    await delay(100)

    return x + 1
  }
  const whenFalse = async x => {
    await delay(100)

    return x + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(5), fn(1) ])
  expect(result).toEqual([ 6, 11 ])
})

test('arity of 2 - condition is async', async () => {
  const condition = async (x, y) => {
    await delay(100)

    return x + y > 4
  }
  const whenTrue = (x, y) => x + y + 1
  const whenFalse = (x, y) => x + y + 10
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

test('arity of 2 - condition is sync', async () => {
  const condition = (x, y) => x + y > 4
  const whenTrue = async (x, y) => {
    await delay(100)

    return x + y + 1
  }
  const whenFalse = async (x, y) => {
    await delay(100)

    return x + y + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

test('arity of 2 - all inputs are async', async () => {
  const condition = async (x, y) => {
    await delay(100)

    return x + y > 4
  }
  const whenTrue = async (x, y) => {
    await delay(100)

    return x + y + 1
  }
  const whenFalse = async (x, y) => {
    await delay(100)

    return x + y + 10
  }
  const fn = ifElseAsync(
    condition, whenTrue, whenFalse
  )
  const result = await Promise.all([ fn(14, 20), fn(1, 3) ])
  expect(result).toEqual([ 35, 14 ])
})

inc

It increments a number.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.inc(1)%20%2F%2F%20%3D%3E%202">Try this <strong>R.inc</strong> example in Rambda REPL</a>

includes

includes<T extends string>(valueToFind: T, input: string): boolean

If input is string, then this method work as native String.includes.

If input is array, then R.equals is used to define if valueToFind belongs to the list.

const result = [
  R.includes('oo', 'foo'),
  R.includes({a: 1}, [{a: 1}])
]
// => [true, true ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.includes('oo'%2C%20'foo')%2C%0A%20%20R.includes(%7Ba%3A%201%7D%2C%20%5B%7Ba%3A%201%7D%5D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%20%5D">Try this <strong>R.includes</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { _indexOf } from './equals.js'

export function includes(valueToFind, iterable){
  if (arguments.length === 1)
    return _iterable => includes(valueToFind, _iterable)
  if (typeof iterable === 'string'){
    return iterable.includes(valueToFind)
  }
  if (!iterable){
    throw new TypeError(`Cannot read property \'indexOf\' of ${ iterable }`)
  }
  if (!isArray(iterable)) return false

  return _indexOf(valueToFind, iterable) > -1
}

import { includes as includesRamda } from 'ramda'

import { includes } from './includes.js'

test('with string as iterable', () => {
  const str = 'foo bar'

  expect(includes('bar')(str)).toBeTrue()
  expect(includesRamda('bar')(str)).toBeTrue()
  expect(includes('never', str)).toBeFalse()
  expect(includesRamda('never', str)).toBeFalse()
})

test('with array as iterable', () => {
  const arr = [ 1, 2, 3 ]

  expect(includes(2)(arr)).toBeTrue()
  expect(includesRamda(2)(arr)).toBeTrue()

  expect(includes(4, arr)).toBeFalse()
  expect(includesRamda(4, arr)).toBeFalse()
})

test('with list of objects as iterable', () => {
  const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]

  expect(includes({ c : 3 }, arr)).toBeTrue()
  expect(includesRamda({ c : 3 }, arr)).toBeTrue()
})

test('with NaN', () => {
  const result = includes(NaN, [ NaN ])
  const ramdaResult = includesRamda(NaN, [ NaN ])
  expect(result).toBeTrue()
  expect(ramdaResult).toBeTrue()
})

test('with wrong input that does not throw', () => {
  const result = includes(1, /foo/g)
  const ramdaResult = includesRamda(1, /foo/g)
  expect(result).toBeFalse()
  expect(ramdaResult).toBeFalse()
})

test('throws on wrong input - match ramda behaviour', () => {
  expect(() => includes(2, null)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of null')
  expect(() => includesRamda(2, null)).toThrowWithMessage(TypeError,
    'Cannot read properties of null (reading \'indexOf\')')
  expect(() => includes(2, undefined)).toThrowWithMessage(TypeError,
    'Cannot read property \'indexOf\' of undefined')
  expect(() => includesRamda(2, undefined)).toThrowWithMessage(TypeError,
    'Cannot read properties of undefined (reading \'indexOf\')')
})

indexBy

It generates object with properties provided by condition and values provided by list array.

If condition is a function, then all list members are passed through it.

If condition is a string, then all list members are passed through R.path(condition).

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%20%7Bid%3A%2010%7D%2C%20%7Bid%3A%2020%7D%20%5D%0A%0Aconst%20withFunction%20%3D%20R.indexBy(%0A%20%20x%20%3D%3E%20x.id%2C%0A%20%20list%0A)%0Aconst%20withString%20%3D%20R.indexBy(%0A%20%20'id'%2C%0A%20%20list%0A)%0Aconst%20result%20%3D%20%5B%0A%20%20withFunction%2C%20%0A%20%20R.equals(withFunction%2C%20withString)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%20%7B%2010%3A%20%7Bid%3A%2010%7D%2C%2020%3A%20%7Bid%3A%2020%7D%20%7D%2C%20true%20%5D">Try this <strong>R.indexBy</strong> example in Rambda REPL</a>

indexOf

It returns the index of the first element of list equals to valueToFind.

If there is no such element, it returns -1.

:boom: It uses R.equals for list of objects/arrays or native indexOf for any other case.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B0%2C%201%2C%202%2C%203%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.indexOf(2%2C%20list)%2C%0A%20%20R.indexOf(0%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5B2%2C%20-1%5D">Try this <strong>R.indexOf</strong> example in Rambda REPL</a>

init

init<T extends unknown[]>(input: T): T extends readonly [...infer U, any] ? U : [...T]

It returns all but the last element of list or string input.

const result = [
  R.init([1, 2, 3]) , 
  R.init('foo')  // => 'fo'
]
// => [[1, 2], 'fo']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.init(%5B1%2C%202%2C%203%5D)%20%2C%20%0A%20%20R.init('foo')%20%20%2F%2F%20%3D%3E%20'fo'%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%202%5D%2C%20'fo'%5D">Try this <strong>R.init</strong> example in Rambda REPL</a>

import baseSlice from './_internals/baseSlice.js'

export function init(listOrString){
  if (typeof listOrString === 'string') return listOrString.slice(0, -1)

  return listOrString.length ?
    baseSlice(
      listOrString, 0, -1
    ) :
    []
}

import { init } from './init.js'

test('with array', () => {
  expect(init([ 1, 2, 3 ])).toEqual([ 1, 2 ])
  expect(init([ 1, 2 ])).toEqual([ 1 ])
  expect(init([ 1 ])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([ 1 ])).toEqual([])
})

test('with string', () => {
  expect(init('foo')).toBe('fo')
  expect(init('f')).toBe('')
  expect(init('')).toBe('')
})

innerJoin

It returns a new list by applying a predicate function to all elements of list1 and list2 and keeping only these elements where predicate returns true.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list1%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0Aconst%20list2%20%3D%20%5B4%2C%205%2C%206%5D%0Aconst%20predicate%20%3D%20(x%2C%20y)%20%3D%3E%20x%20%3E%3D%20y%0Aconst%20result%20%3D%20R.innerJoin(predicate%2C%20list1%2C%20list2)%0A%2F%2F%20%3D%3E%20%5B4%2C%205%5D">Try this <strong>R.innerJoin</strong> example in Rambda REPL</a>

insert

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%2C%20'd'%2C%20'e'%5D%3B%0Aconst%20result%20%3D%20R.insert(2%2C%20'x'%2C%20list)%3B%0A%2F%2F%20%3D%3E%20%5B'a'%2C%20'b'%2C%20'x'%2C%20'c'%2C%20'd'%2C%20'e'%5D">Try this <strong>R.insert</strong> example in Rambda REPL</a>

insertAll

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%2C%20'd'%2C%20'e'%5D%3B%0Aconst%20result%20%3D%20R.insertAll(2%2C%20%5B'x'%2C%20'y'%2C%20'z'%5D%2C%20list)%3B%0A%2F%2F%20%3D%3E%20%5B'a'%2C%20'b'%2C%20'x'%2C%20'y'%2C%20'z'%2C%20'c'%2C%20'd'%2C%20'e'%5D">Try this <strong>R.insertAll</strong> example in Rambda REPL</a>

interpolate

interpolate(inputWithTags: string, templateArguments: object): string

It generates a new string from inputWithTags by replacing all {{x}} occurrences with values provided by templateArguments.

const inputWithTags = 'foo is {{bar}} even {{a}} more'
const templateArguments = {"bar":"BAR", a: 1}

const result = R.interpolate(inputWithTags, templateArguments)
const expected = 'foo is BAR even 1 more'
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20inputWithTags%20%3D%20'foo%20is%20%7B%7Bbar%7D%7D%20even%20%7B%7Ba%7D%7D%20more'%0Aconst%20templateArguments%20%3D%20%7B%22bar%22%3A%22BAR%22%2C%20a%3A%201%7D%0A%0Aconst%20result%20%3D%20R.interpolate(inputWithTags%2C%20templateArguments)%0Aconst%20expected%20%3D%20'foo%20is%20BAR%20even%201%20more'%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.interpolate</strong> example in Rambda REPL</a>

const getOccurrences = input => input.match(/{{\s*.+?\s*}}/g)

const getOccurrenceProp = occurrence =>
  occurrence.replace(/{{\s*|\s*}}/g, '')

const replace = ({ inputHolder, prop, replacer }) => {
  const regexBase = `{{${ prop }}}`
  const regex = new RegExp(regexBase, 'g')

  return inputHolder.replace(regex, replacer)
}

export function interpolate(input, templateInput){
  if (arguments.length === 1){
    return _templateInput => interpolate(input, _templateInput)
  }

  const occurrences = getOccurrences(input)
  if (occurrences === null) return input
  let inputHolder = input

  for (const occurrence of occurrences){
    const prop = getOccurrenceProp(occurrence)

    inputHolder = replace({
      inputHolder,
      prop,
      replacer : templateInput[ prop ],
    })
  }

  return inputHolder
}

import { interpolate } from './interpolate.js'

test('within bracets', () => {
  const input = 'foo is { {{bar}} } even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = interpolate(input, templateInput)
  const expectedResult = 'foo is { BAR } even 1 more'

  expect(result).toEqual(expectedResult)
})

test('happy', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    bar : 'BAR',
    a   : 1,
  }

  const result = interpolate(input, templateInput)
  const expectedResult = 'foo is BAR even 1 more'

  expect(result).toEqual(expectedResult)
})

test('no interpolation + curry', () => {
  const input = 'foo is bar even more'
  const templateInput = { bar : 'BAR' }

  const result = interpolate(input)(templateInput)
  const expectedResult = 'foo is bar even more'

  expect(result).toEqual(expectedResult)
})

test('with missing template input', () => {
  const input = 'foo is {{bar}} even {{a}} more'
  const templateInput = {
    baz : 'BAR',
    a   : 1,
  }

  const result = interpolate(input, templateInput)
  const expectedResult = 'foo is undefined even 1 more'

  expect(result).toEqual(expectedResult)
})

test('with arbitrary expression', () => {
  const input = '1 + 2 = {{ 1 + 2 }}'
  const templateInput = {}

  const result = interpolate(input, templateInput)

  expect(result).toEqual(input)
})

intersection

It loops through listA and listB and returns the intersection of the two according to R.equals.

:boom: There is slight difference between Rambda and Ramda implementation. Ramda.intersection(['a', 'b', 'c'], ['c', 'b']) result is "[ 'c', 'b' ]", but Rambda result is "[ 'b', 'c' ]".

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20listA%20%3D%20%5B%20%7B%20id%20%3A%201%20%7D%2C%20%7B%20id%20%3A%202%20%7D%2C%20%7B%20id%20%3A%203%20%7D%2C%20%7B%20id%20%3A%204%20%7D%20%5D%0Aconst%20listB%20%3D%20%5B%20%7B%20id%20%3A%203%20%7D%2C%20%7B%20id%20%3A%204%20%7D%2C%20%7B%20id%20%3A%205%20%7D%2C%20%7B%20id%20%3A%206%20%7D%20%5D%0A%0Aconst%20result%20%3D%20R.intersection(listA%2C%20listB)%0A%2F%2F%20%3D%3E%20%5B%7B%20id%20%3A%203%20%7D%2C%20%7B%20id%20%3A%204%20%7D%5D">Try this <strong>R.intersection</strong> example in Rambda REPL</a>

intersperse

It adds a separator between members of list.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%200%2C%201%2C%202%2C%203%20%5D%0Aconst%20separator%20%3D%20'%7C'%0Aconst%20result%20%3D%20intersperse(separator%2C%20list)%0A%2F%2F%20%3D%3E%20%5B0%2C%20'%7C'%2C%201%2C%20'%7C'%2C%202%2C%20'%7C'%2C%203%5D">Try this <strong>R.intersperse</strong> example in Rambda REPL</a>

is

It returns true if x is instance of targetPrototype.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.is(String%2C%20'foo')%2C%20%20%0A%20%20R.is(Array%2C%201)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.is</strong> example in Rambda REPL</a>

isEmpty

isEmpty<T>(x: T): boolean

It returns true if x is empty.

const result = [
  R.isEmpty(''),
  R.isEmpty({ x : 0 })
]
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.isEmpty('')%2C%0A%20%20R.isEmpty(%7B%20x%20%3A%200%20%7D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.isEmpty</strong> example in Rambda REPL</a>

import { type } from './type.js'

export function isEmpty(input){
  const inputType = type(input)
  if ([ 'Undefined', 'NaN', 'Number', 'Null' ].includes(inputType))
    return false
  if (!input) return true

  if (inputType === 'Object'){
    return Object.keys(input).length === 0
  }

  if (inputType === 'Array'){
    return input.length === 0
  }

  return false
}

import { isEmpty } from './isEmpty.js'

test('happy', () => {
  expect(isEmpty(undefined)).toBeFalse()
  expect(isEmpty('')).toBeTrue()
  expect(isEmpty(null)).toBeFalse()
  expect(isEmpty(' ')).toBeFalse()
  expect(isEmpty(new RegExp(''))).toBeFalse()
  expect(isEmpty([])).toBeTrue()
  expect(isEmpty([ [] ])).toBeFalse()
  expect(isEmpty({})).toBeTrue()
  expect(isEmpty({ x : 0 })).toBeFalse()
  expect(isEmpty(0)).toBeFalse()
  expect(isEmpty(NaN)).toBeFalse()
  expect(isEmpty([ '' ])).toBeFalse()
})

isNil

isNil(x: any): x is null | undefined

It returns true if x is either null or undefined.

const result = [
  R.isNil(null),
  R.isNil(1),
]
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.isNil(null)%2C%0A%20%20R.isNil(1)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.isNil</strong> example in Rambda REPL</a>

export function isNil(x){
  return x === undefined || x === null
}

import { isNil } from './isNil.js'

test('happy', () => {
  expect(isNil(null)).toBeTrue()

  expect(isNil(undefined)).toBeTrue()

  expect(isNil([])).toBeFalse()
})

isNotEmpty

isNotEmpty<T>(value: T[]): value is NonEmptyArray<T>

isNotNil

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.isNotNil(null)%2C%0A%20%20R.isNotNil(undefined)%2C%0A%20%20R.isNotNil(%5B%5D)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20false%2C%20true%5D">Try this <strong>R.isNotNil</strong> example in Rambda REPL</a>

isPromise

isPromise(input: any): boolean

isType

isType(targetType: RambdaTypes, input: any): boolean

It returns true if targetType is equal to type of input according to R.type.

R.isType('Async',R.delay(1000))
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.isType('Async'%2CR.delay(1000))%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.isType</strong> example in Rambda REPL</a>

import { type } from './type.js'

export function isType(xType, x){
  if (arguments.length === 1){
    return xHolder => isType(xType, xHolder)
  }

  return type(x) === xType
}

import { delay } from './delay.js'
import { isType } from './isType.js'

const list = [ 1, 2, 3 ]

test('array', () => {
  expect(isType('Array', list)).toBeTruthy()
  expect(isType('Array')([])).toBeTruthy()
})

test('promise', () => {
  expect(isType('Promise', Promise.resolve(1))).toBeTruthy()
})

test('async', () => {
  async function fn(){}

  expect(isType('Promise', fn)).toBeTruthy()
})

test('with R.delay', () => {
  expect(isType('Function', delay)).toBeTruthy()
  expect(isType('Promise', delay(100))).toBeTruthy()
})

isValid

isValid({input: object, schema: Schema}: IsValid): boolean

It checks if input is following schema specifications.

If validation fails, it returns false.

Please check the detailed explanation as it is hard to write a short description for this method.

:boom: Independently, somebody else came with very similar idea called superstruct

const input = {a: ['foo', 'bar']}
const invalidInput = {a: ['foo', 'bar', 1]}
const schema = {a: [String]}
const result = [
  R.isValid({schema, input}),
  R.isValid({schema, input: invalidInput})
]
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20input%20%3D%20%7Ba%3A%20%5B'foo'%2C%20'bar'%5D%7D%0Aconst%20invalidInput%20%3D%20%7Ba%3A%20%5B'foo'%2C%20'bar'%2C%201%5D%7D%0Aconst%20schema%20%3D%20%7Ba%3A%20%5BString%5D%7D%0Aconst%20result%20%3D%20%5B%0A%20%20R.isValid(%7Bschema%2C%20input%7D)%2C%0A%20%20R.isValid(%7Bschema%2C%20input%3A%20invalidInput%7D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.isValid</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { all } from './all.js'
import { any } from './any.js'
import { includes } from './includes.js'
import { init } from './init.js'
import { test } from './test.js'
import { toLower } from './toLower.js'
import { type } from './type.js'

export function isPrototype(input){
  const currentPrototype = input.prototype
  const list = [ Number, String, Boolean, Promise ]
  let toReturn = false
  let counter = -1
  while (++counter < list.length && !toReturn){
    if (currentPrototype === list[ counter ].prototype) toReturn = true
  }

  return toReturn
}

export function prototypeToString(input){
  const currentPrototype = input.prototype
  const list = [ Number, String, Boolean, Promise ]
  const translatedList = [ 'Number', 'String', 'Boolean', 'Promise' ]
  let found
  let counter = -1

  while (++counter < list.length){
    if (currentPrototype === list[ counter ].prototype) found = counter
  }

  return translatedList[ found ]
}

const typesWithoutPrototype = [ 'any', 'promise', 'async', 'function' ]

export function fromPrototypeToString(rule){
  if (
    isArray(rule) ||
    rule === undefined ||
    rule === null ||
    rule.prototype === undefined ||
    typesWithoutPrototype.includes(rule)
  ){
    return {
      rule,
      parsed : false,
    }
  }
  if (String.prototype === rule.prototype){
    return {
      rule   : 'string',
      parsed : true,
    }
  }
  if (Boolean.prototype === rule.prototype){
    return {
      rule   : 'boolean',
      parsed : true,
    }
  }
  if (Number.prototype === rule.prototype){
    return {
      rule   : 'number',
      parsed : true,
    }
  }

  return {
    rule   : type(rule.prototype).toLowerCase(),
    parsed : true,
  }
}

function getRuleAndType(schema, requirementRaw){
  const ruleRaw = schema[ requirementRaw ]
  const typeIs = type(ruleRaw)
  const { rule, parsed } = fromPrototypeToString(ruleRaw)

  return {
    rule,
    ruleType : parsed ? 'String' : typeIs,
  }
}

export function isValid({ input, schema }){
  if (input === undefined || schema === undefined) return false

  let flag = true
  const boom = boomFlag => {
    if (!boomFlag){
      flag = false
    }
  }

  for (const requirementRaw in schema){
    if (flag){
      const isOptional = requirementRaw.endsWith('?')
      const requirement = isOptional ? init(requirementRaw) : requirementRaw

      const { rule, ruleType } = getRuleAndType(schema, requirementRaw)
      const inputProp = input[ requirement ]
      const inputPropType = type(input[ requirement ])

      const ok = isOptional && inputProp !== undefined || !isOptional

      if (!ok || rule === 'any' && inputProp != null || rule === inputProp)
        continue

      if (ruleType === 'Object'){
        /**
         * This rule is standalone schema, so we recursevly call `isValid`
         */
        const isValidResult = isValid({
          input  : inputProp,
          schema : rule,
        })
        boom(isValidResult)
      } else if (ruleType === 'String'){
        /**
         * Rule is actual rule such as 'number', so the two types are compared
         */
        boom(toLower(inputPropType) === rule)
      } else if (typeof rule === 'function'){
        /**
         * Rule is function so we pass to it the input
         */
        boom(rule(inputProp))
      } else if (ruleType === 'Array' && inputPropType === 'String'){
        /**
         * Enum case | rule is like a: ['foo', 'bar']
         */
        boom(includes(inputProp, rule))
      } else if (
        ruleType === 'Array' &&
        rule.length === 1 &&
        inputPropType === 'Array'
      ){
        /**
         * 1. array of type | rule is like a: ['number']
         * 2. rule is like a: [{foo: 'string', bar: 'number'}]
         */
        const [ currentRule ] = rule
        const currentRuleType = type(currentRule)

        //Check if rule is invalid
        boom(currentRuleType === 'String' ||
            currentRuleType === 'Object' ||
            isPrototype(currentRule))

        if (currentRuleType === 'Object' && flag){
          /**
           * 2. rule is like a: [{from: 'string'}]
           */
          const isValidResult = all(inputPropInstance =>
            isValid({
              input  : inputPropInstance,
              schema : currentRule,
            }),
          inputProp)
          boom(isValidResult)
        } else if (flag){
          /**
           * 1. array of type
           */

          const actualRule =
            currentRuleType === 'String' ?
              currentRule :
              prototypeToString(currentRule)
          const isInvalidResult = any(inputPropInstance =>
            type(inputPropInstance).toLowerCase() !==
              actualRule.toLowerCase(),
          inputProp)
          boom(!isInvalidResult)
        }
      } else if (ruleType === 'RegExp' && inputPropType === 'String'){
        boom(test(rule, inputProp))
      } else {
        boom(false)
      }
    }
  }

  return flag
}

import { delay } from './delay.js'
import { isPrototype, isValid } from './isValid.js'

test('is prototype', () => {
  expect(isPrototype(Promise)).toBeTrue()
  expect(isPrototype(Number)).toBeTrue()
  expect(isPrototype(Boolean)).toBeTrue()
  expect(isPrototype(String)).toBeTrue()
  expect(isPrototype(0)).toBeFalse()
})

test('prototype inside array', () => {
  const input = { a : [ 1, 2, 3, 4 ] }
  const schema = { a : [ Number ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('with Promise prototype', () => {
  const input = { a : [ delay(1), delay(2) ] }
  const schema = { a : [ Promise ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('object prototype as rule - true', () => {
  const input = { a : {} }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('list of functions', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ 'function' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function schema type can be only string', () => {
  const input = { a : [ () => {}, delay ] }
  const schema = { a : [ Function ] }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('object prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Object }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('number prototype as rule - true', () => {
  const input = { a : 1 }
  const schema = { a : Number }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - true', () => {
  const input = { a : [ 1, 2, 3 ] }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('array prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Array }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('string prototype as rule - true', () => {
  const input = { a : 'foo' }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('string prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : String }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('boolean prototype as rule - true', () => {
  const input = { a : true }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('boolean prototype as rule - false', () => {
  const input = { a : null }
  const schema = { a : Boolean }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex prototype cannot be rule - true', () => {
  const input = { a : /foo/g }
  const schema = { a : new RegExp('foo') }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('undefined as a rule - true', () => {
  const input = { a : undefined }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('undefined as a rule - false', () => {
  const input = { a : null }
  const schema = { a : undefined }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('null as a rule - true', () => {
  const input = { a : null }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('null as a rule - false', () => {
  const input = { a : undefined }
  const schema = { a : null }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `null`', () => {
  const input = { a : null }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('`any` safeguard against `undefined`', () => {
  const input = { a : undefined }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('type can be `"any"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'any' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `"function"`', () => {
  const input = { a : () => {} }
  const schema = { a : 'function' }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise`', () => {
  const input = {
    a : delay(1999),
    b : async () => {},
  }
  const schema = {
    a : 'promise',
    b : 'promise',
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('type can be `promise` list', () => {
  const input = { a : [ delay(1999) ] }
  const schema = { a : [ 'promise' ] }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('function as schema - false', () => {
  const input = {
    a : {
      ab : () => true,
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('regex ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /fo/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('regex !ok', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : /ba/,
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props is missing', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    'a' : {
      ab : 'string',
      ac : 'number',
    },
    'b?' : 'string',
    'c'  : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('optional props - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 3,
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is missing - nested', () => {
  const input = {
    a : { ab : 'foo' },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('optional props is wrong type - nested', () => {
  const input = {
    a : {
      ab : 'foo',
      ac : 'bar',
    },
    b : [],
    c : [ 1, 2 ],
  }
  const schema = {
    a : {
      'ab'  : 'string',
      'ac?' : 'number',
    },
    b : 'array',
    c : [ 'number' ],
  }
  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('nested schema', () => {
  const input = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 'foo',
  }
  const schema = {
    a : {
      b : 'string',
      c : 'number',
      d : 'string',
    },
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInputFirst = {
    a : {
      b : 'str',
      c : 3,
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()

  const invalidInputSecond = {
    a : {
      b : 'str',
      c : 'str',
      d : 'str',
    },
    b : 5,
  }

  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()

  const invalidInputThird = {
    a : { b : 'str' },
    b : 5,
  }

  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('array of type', () => {
  const input = {
    a : [ 1, 2 ],
    b : 'foo',
  }
  const schema = {
    a : [ 'number' ],
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  const invalidInput = {
    a : [ 1, '1' ],
    b : 'foo',
  }

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('function as rule', () => {
  const input = {
    a : [ 1, 2, 3, 4 ],
    b : 'foo',
  }
  const invalidInput = {
    a : [ 4 ],
    b : 'foo',
  }

  const schema = {
    a : x => x.length > 2,
    b : 'string',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('input prop is undefined', () => {
  const input = { b : 3 }
  const schema = { a : 'number' }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()
})

test('enum', () => {
  const input = { a : 'foo' }
  const invalidInput = { a : '' }

  const schema = { a : [ 'foo', 'bar', 'baz' ] }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInput,
    schema,
  })).toBeFalsy()
})

test('readme example', () => {
  const basicSchema = { a : [ 'string' ] }
  const schema = {
    b : [ basicSchema ],
    c : {
      d : { e : 'boolean' },
      f : 'array',
    },
    g : [ 'foo', 'bar', 'baz' ],
  }
  const input = {
    b : [ { a : [ 'led', 'zeppelin' ] } ],
    c : {
      d : { e : true },
      f : [ 'any', 1, null, 'value' ],
    },
    g : 'foo',
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('should allow additional properties', () => {
  const input = {
    title : 'You shook me',
    year  : 1969,
  }

  expect(isValid({
    input,
    schema : { title : 'string' },
  })).toBeTruthy()
})

test('accepts values as schemas', () => {
  const input = {
    title : 'You shook me',
    genre : 'Blues',
    year  : 1969,
  }
  const schema = {
    title : 'You shook me',
    year  : 1969,
  }
  expect(isValid({
    input,
    schema,
  })).toBeTruthy()
})

test('compatible schemas with nested object', () => {
  const input = {
    foo : 'bar',
    baz : { a : { b : 'c' } },
  }
  const invalidInputFirst = {
    foo : 'bar',
    baz : { a : { b : 1 } },
  }
  const invalidInputSecond = {
    foo : 'bar',
    baz : { a : { b : [] } },
  }
  const invalidInputThird = {
    foo : 'bar',
    baz : { a : { b : null } },
  }
  const schema = {
    foo : 'string',
    baz : { a : { b : 'string' } },
  }

  expect(isValid({
    input,
    schema,
  })).toBeTruthy()

  expect(isValid({
    input : invalidInputFirst,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputSecond,
    schema,
  })).toBeFalsy()
  expect(isValid({
    input : invalidInputThird,
    schema,
  })).toBeFalsy()
})

test('should return true when schema is empty object', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : {},
  })).toBeTruthy()
})

test('when schema is undefined', () => {
  expect(isValid({
    input  : { a : 1 },
    schema : undefined,
  })).toBeFalsy()
})

test('should return false with invalid schema rule', () => {
  const input = {
    foo : 'bar',
    a   : {},
  }
  const inputSecond = { foo : 'bar' }

  const schema = {
    foo : 'string',
    baz : { a : {} },
  }

  expect(isValid({
    input,
    schema,
  })).toBeFalsy()

  expect(isValid({
    input : inputSecond,
    schema,
  })).toBeFalsy()
})

test('array of schemas', () => {
  const input = {
    b : [
      {
        a : 'led',
        b : 1,
      },
      {
        a : 'dancing',
        b : 1,
      },
    ],
  }
  const basicSchema = {
    a : String,
    b : Number,
  }
  const schema = { b : [ basicSchema ] }
  const result = isValid({
    input,
    schema,
  })

  expect(result).toBeTruthy()
})

isValidAsync

isValidAsync(x: IsValidAsync): Promise<boolean>

Asynchronous version of R.isValid

const input = {a: 1, b: 2}
const invalidInput = {a: 1, b: 'foo'}
const schema = {a: Number, b: async x => {
  await R.delay(100)
  return typeof x === 'number'
}}

const result = await Promise.all([
  R.isValidAsync({schema, input}),
  R.isValidAsync({schema, input: invalidInput})
])
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20input%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0Aconst%20invalidInput%20%3D%20%7Ba%3A%201%2C%20b%3A%20'foo'%7D%0Aconst%20schema%20%3D%20%7Ba%3A%20Number%2C%20b%3A%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20typeof%20x%20%3D%3D%3D%20'number'%0A%7D%7D%0A%0Aconst%20result%20%3D%20await%20Promise.all(%5B%0A%20%20R.isValidAsync(%7Bschema%2C%20input%7D)%2C%0A%20%20R.isValidAsync(%7Bschema%2C%20input%3A%20invalidInput%7D)%0A%5D)%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.isValidAsync</strong> example in Rambda REPL</a>

import { forEach } from './forEach.js'
import { isPromise } from './isPromise.js'
import { isValid } from './isValid.js'

export async function isValidAsync({ schema, input }){
  const asyncSchema = {}
  const simpleSchema = {}
  forEach((rule, prop) => {
    if (isPromise(rule)){
      asyncSchema[ prop ] = rule
    } else {
      simpleSchema[ prop ] = rule
    }
  }, schema)

  if (Object.keys(asyncSchema).length === 0)
    return isValid({
      input,
      schema,
    })

  if (
    !isValid({
      input,
      schema : simpleSchema,
    })
  )
    return false

  let toReturn = true

  for (const singleRuleProp in asyncSchema){
    if (toReturn){
      const validated = await asyncSchema[ singleRuleProp ](input[ singleRuleProp ])
      if (!validated) toReturn = false
    }
  }

  return toReturn
}

import { result } from 'lodash'

import { delay } from './delay.js'
import { isValidAsync } from './isValidAsync.js'

const simplePredicate = async x => {
  await delay(100)

  return x > 5
}

test('happy', async () => {
  const input = {
    a          : 1,
    b          : 7,
    c          : 9,
    additional : 'foo',
  }
  const invalidInput = {
    a : 1,
    b : 2,
    c : 9,
  }
  const schema = {
    a : Number,
    b : simplePredicate,
    c : simplePredicate,
  }
  const invalidSchema = {
    a : Boolean,
    b : simplePredicate,
    c : simplePredicate,
  }
  const result = await isValidAsync({
    input,
    schema,
  })
  const invalidResult = await isValidAsync({
    input,
    schema : invalidSchema,
  })
  const withInvalidInput = await isValidAsync({
    input : invalidInput,
    schema,
  })
  expect(result).toBeTruthy()
  expect(invalidResult).toBeFalsy()
  expect(withInvalidInput).toBeFalsy()
})

test('without async rules', async () => {
  const input = {
    a : 1,
    b : 7,
  }
  const schema = {
    a : Number,
    b : x => x > 2,
  }
  const invalidSchema = {
    a : Number,
    b : Boolean,
  }
  const result = await isValidAsync({
    input,
    schema,
  })
  const invalidResult = await isValidAsync({
    input,
    schema : invalidSchema,
  })

  expect(result).toBeTruthy()
  expect(invalidResult).toBeFalsy()
})

test('readme example', async () => {
  const input = {
    a : 1,
    b : 2,
  }
  const invalidInput = {
    a : 1,
    b : 'foo',
  }
  const schema = {
    a : Number,
    b : async x => {
      await delay(100)

      return typeof x === 'number'
    },
  }
  const result = await Promise.all([
    isValidAsync({
      schema,
      input,
    }),
    isValidAsync({
      schema,
      input : invalidInput,
    }),
  ])
  expect(result).toEqual([ true, false ])
})

join

join<T>(glue: string, list: T[]): string

It returns a string of all list instances joined with a glue.

R.join('-', [1, 2, 3])  // => '1-2-3'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.join('-'%2C%20%5B1%2C%202%2C%203%5D)%20%20%2F%2F%20%3D%3E%20'1-2-3'">Try this <strong>R.join</strong> example in Rambda REPL</a>

export function join(glue, list){
  if (arguments.length === 1) return _list => join(glue, _list)

  return list.join(glue)
}

import { join } from './join.js'

test('curry', () => {
  expect(join('|')([ 'foo', 'bar', 'baz' ])).toBe('foo|bar|baz')

  expect(join('|', [ 1, 2, 3 ])).toBe('1|2|3')

  const spacer = join(' ')

  expect(spacer([ 'a', 2, 3.4 ])).toBe('a 2 3.4')
})

juxt

juxt<A extends any[], R1>(fns: [(...a: A) => R1]): (...a: A) => [R1]

It applies list of function to a list of inputs.

const getRange = juxt([ Math.min, Math.max, Math.min ])
const result = getRange(
  3, 4, 9, -3
)
// => [-3, 9, -3]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20getRange%20%3D%20juxt(%5B%20Math.min%2C%20Math.max%2C%20Math.min%20%5D)%0Aconst%20result%20%3D%20getRange(%0A%20%203%2C%204%2C%209%2C%20-3%0A)%0A%2F%2F%20%3D%3E%20%5B-3%2C%209%2C%20-3%5D">Try this <strong>R.juxt</strong> example in Rambda REPL</a>

export function juxt(listOfFunctions){
  return (...args) => listOfFunctions.map(fn => fn(...args))
}

import { juxt } from './juxt.js'

test('happy', () => {
  const fn = juxt([ Math.min, Math.max, Math.min ])
  const result = fn(
    3, 4, 9, -3
  )
  expect(result).toEqual([ -3, 9, -3 ])
})

keys

keys<T extends object>(x: T): (keyof T & string)[]

It applies Object.keys over x and returns its keys.

R.keys({a:1, b:2})  // => ['a', 'b']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.keys(%7Ba%3A1%2C%20b%3A2%7D)%20%20%2F%2F%20%3D%3E%20%5B'a'%2C%20'b'%5D">Try this <strong>R.keys</strong> example in Rambda REPL</a>

export function keys(x){
  return Object.keys(x)
}

import { keys } from './keys.js'

test('happy', () => {
  expect(keys({ a : 1 })).toEqual([ 'a' ])
})

last

last(str: ''): undefined

It returns the last element of input, as the input can be either a string or an array. It returns undefined if array has length of 0.

const result = [
  R.last([1, 2, 3]),
  R.last('foo'),
]
// => [3, 'o']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.last(%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.last('foo')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B3%2C%20'o'%5D">Try this <strong>R.last</strong> example in Rambda REPL</a>

export function last(listOrString){
  if (typeof listOrString === 'string'){
    return listOrString[ listOrString.length - 1 ] || ''
  }

  return listOrString[ listOrString.length - 1 ]
}

import { last } from './last.js'

test('with list', () => {
  expect(last([ 1, 2, 3 ])).toBe(3)
  expect(last([])).toBeUndefined()
})

test('with string', () => {
  expect(last('abc')).toBe('c')
  expect(last('')).toBe('')
})

lastIndexOf

lastIndexOf<T>(target: T, list: T[]): number

It returns the last index of target in list array.

R.equals is used to determine equality between target and members of list.

If there is no such index, then -1 is returned.

const list = [1, 2, 3, 1, 2, 3]
const result = [
  R.lastIndexOf(2, list),
  R.lastIndexOf(4, list),
]
// => [4, -1]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%201%2C%202%2C%203%5D%0Aconst%20result%20%3D%20%5B%0A%20%20R.lastIndexOf(2%2C%20list)%2C%0A%20%20R.lastIndexOf(4%2C%20list)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B4%2C%20-1%5D">Try this <strong>R.lastIndexOf</strong> example in Rambda REPL</a>

import { _lastIndexOf } from './equals.js'

export function lastIndexOf(valueToFind, list){
  if (arguments.length === 1){
    return _list => _lastIndexOf(valueToFind, _list)
  }

  return _lastIndexOf(valueToFind, list)
}

import { lastIndexOf as lastIndexOfRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { possibleIterables, possibleTargets } from './indexOf.spec.js'
import { lastIndexOf } from './lastIndexOf.js'

test('with NaN', () => {
  expect(lastIndexOf(NaN, [ NaN ])).toBe(0)
})

test('will throw with bad input', () => {
  expect(lastIndexOfRamda([], true)).toBe(-1)
  expect(() => indexOf([], true)).toThrowErrorMatchingInlineSnapshot('"indexOf is not defined"')
})

test('without list of objects - no R.equals', () => {
  expect(lastIndexOf(3, [ 1, 2, 3, 4 ])).toBe(2)
  expect(lastIndexOf(10)([ 1, 2, 3, 4 ])).toBe(-1)
})

test('list of objects uses R.equals', () => {
  const listOfObjects = [ { a : 1 }, { b : 2 }, { c : 3 } ]
  expect(lastIndexOf({ c : 4 }, listOfObjects)).toBe(-1)
  expect(lastIndexOf({ c : 3 }, listOfObjects)).toBe(2)
})

test('list of arrays uses R.equals', () => {
  const listOfLists = [ [ 1 ], [ 2, 3 ], [ 2, 3, 4 ], [ 2, 3 ], [ 1 ], [] ]
  expect(lastIndexOf([], listOfLists)).toBe(5)
  expect(lastIndexOf([ 1 ], listOfLists)).toBe(4)
  expect(lastIndexOf([ 2, 3, 4 ], listOfLists)).toBe(2)
  expect(lastIndexOf([ 2, 3, 5 ], listOfLists)).toBe(-1)
})

test('with string as iterable', () => {
  expect(() => lastIndexOf('a', 'abc')).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of abc"')
  expect(lastIndexOfRamda('a', 'abc')).toBe(0)
})

describe('brute force', () => {
  compareCombinations({
    fn          : lastIndexOf,
    fnRamda     : lastIndexOfRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 34,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 170,
        }
      `)
    },
  })
})

length

length<T>(input: T[]): number

It returns the length property of list or string input.

const result = [
  R.length([1, 2, 3, 4]),
  R.length('foo'),
]
// => [4, 3]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.length(%5B1%2C%202%2C%203%2C%204%5D)%2C%0A%20%20R.length('foo')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B4%2C%203%5D">Try this <strong>R.length</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

export function length(x){
  if (isArray(x)) return x.length
  if (typeof x === 'string') return x.length

  return NaN
}

import { length as lengthRamda } from 'ramda'

import { length } from './length.js'

test('happy', () => {
  expect(length('foo')).toBe(3)
  expect(length([ 1, 2, 3 ])).toBe(3)
  expect(length([])).toBe(0)
})

test('with empty string', () => {
  expect(length('')).toBe(0)
})

test('with bad input returns NaN', () => {
  expect(length(0)).toBeNaN()
  expect(length({})).toBeNaN()
  expect(length(null)).toBeNaN()
  expect(length(undefined)).toBeNaN()
})

test('with length as property', () => {
  const input1 = { length : '123' }
  const input2 = { length : null }
  const input3 = { length : '' }

  expect(length(input1)).toBeNaN()
  expect(lengthRamda(input1)).toBeNaN()
  expect(length(input2)).toBeNaN()
  expect(lengthRamda(input2)).toBeNaN()
  expect(length(input3)).toBeNaN()
  expect(lengthRamda(input3)).toBeNaN()
})

lens

lens<S, A>(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens<S, A>

It returns a lens for the given getter and setter functions.

The getter gets the value of the focus; the setter sets the value of the focus.

The setter should not mutate the data structure.

const xLens = R.lens(R.prop('x'), R.assoc('x'));

R.view(xLens, {x: 1, y: 2}) // => 1
R.set(xLens, 4, {x: 1, y: 2}) // => {x: 4, y: 2}
R.over(xLens, R.negate, {x: 1, y: 2}) // => {x: -1, y: 2}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20xLens%20%3D%20R.lens(R.prop('x')%2C%20R.assoc('x'))%3B%0A%0AR.view(xLens%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%201%0AR.set(xLens%2C%204%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%20%7Bx%3A%204%2C%20y%3A%202%7D%0Aconst%20result%20%3D%20R.over(xLens%2C%20R.negate%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%20%7Bx%3A%20-1%2C%20y%3A%202%7D">Try this <strong>R.lens</strong> example in Rambda REPL</a>

export function lens(getter, setter){
  return function (functor){
    return function (target){
      return functor(getter(target)).map(focus => setter(focus, target))
    }
  }
}

lensEq

lensEq(lens: Function, value: any, data: any): boolean

It returns true if data structure focused by the given lens equals to the target value.

R.equals is used to determine equality.

:boom: Idea for this method comes from ramda-adjunct library

const list = [ 1, 2, 3 ]
const lens = R.lensIndex(0)
const result = R.lensEq(
  lens, 1, list
)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%201%2C%202%2C%203%20%5D%0Aconst%20lens%20%3D%20R.lensIndex(0)%0Aconst%20result%20%3D%20R.lensEq(%0A%20%20lens%2C%201%2C%20list%0A)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.lensEq</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { equals } from './equals.js'
import { view } from './view.js'

function lensEqFn(
  lens, target, input
){
  return equals(view(lens, input), target)
}

export const lensEq = curry(lensEqFn)

import { lensEq } from './lensEq.js'
import { lensIndex } from './lensIndex.js'
import { lensPath } from './lensPath.js'

test('with list', () => {
  const list = [ 1, 2, 3 ]
  const lens = lensIndex(0)
  expect(lensEq(
    lens, 1, list
  )).toBeTrue()
  expect(lensEq(lens, 2)(list)).toBeFalse()
})

test('with R.lensPath', () => {
  const input = { a : { b : { c : 1 } } }
  const target = { c : 1 }
  const lens = lensPath('a.b')

  expect(lensEq(lens)(target)(input)).toBeTrue()
  expect(lensEq(
    lens, target, { c : 2 }
  )).toBeFalse()
})

lensIndex

lensIndex<A>(n: number): Lens<A[], A>

It returns a lens that focuses on specified index.

const list = ['a', 'b', 'c']
const headLens = R.lensIndex(0)

R.view(headLens, list) // => 'a'
R.set(headLens, 'x', list) // => ['x', 'b', 'c']
R.over(headLens, R.toUpper, list) // => ['A', 'b', 'c']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%5D%0Aconst%20headLens%20%3D%20R.lensIndex(0)%0A%0AR.view(headLens%2C%20list)%20%2F%2F%20%3D%3E%20'a'%0AR.set(headLens%2C%20'x'%2C%20list)%20%2F%2F%20%3D%3E%20%5B'x'%2C%20'b'%2C%20'c'%5D%0Aconst%20result%20%3D%20R.over(headLens%2C%20R.toUpper%2C%20list)%20%2F%2F%20%3D%3E%20%5B'A'%2C%20'b'%2C%20'c'%5D">Try this <strong>R.lensIndex</strong> example in Rambda REPL</a>

import { lens } from './lens.js'
import { nth } from './nth.js'
import { update } from './update.js'

export function lensIndex(index){
  return lens(nth(index), update(index))
}

import { compose } from './compose.js'
import { keys } from './keys.js'
import { lensIndex } from './lensIndex.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'

const testList = [ { a : 1 }, { b : 2 }, { c : 3 } ]

test('focuses list element at the specified index', () => {
  expect(view(lensIndex(0), testList)).toEqual({ a : 1 })
})

test('returns undefined if the specified index does not exist', () => {
  expect(view(lensIndex(10), testList)).toBeUndefined()
})

test('sets the list value at the specified index', () => {
  expect(set(
    lensIndex(0), 0, testList
  )).toEqual([ 0, { b : 2 }, { c : 3 } ])
})

test('applies function to the value at the specified list index', () => {
  expect(over(
    lensIndex(2), keys, testList
  )).toEqual([ { a : 1 }, { b : 2 }, [ 'c' ] ])
})

test('can be composed', () => {
  const nestedList = [ 0, [ 10, 11, 12 ], 1, 2 ]
  const composedLens = compose(lensIndex(1), lensIndex(0))

  expect(view(composedLens, nestedList)).toBe(10)
})

test('set s (get s) === s', () => {
  expect(set(
    lensIndex(0), view(lensIndex(0), testList), testList
  )).toEqual(testList)
})

test('get (set s v) === v', () => {
  expect(view(lensIndex(0), set(
    lensIndex(0), 0, testList
  ))).toBe(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensIndex(0),
    set(
      lensIndex(0), 11, set(
        lensIndex(0), 10, testList
      )
    ))).toBe(11)
})

lensPath

It returns a lens that focuses on specified path.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20lensPath%20%3D%20R.lensPath(%5B'x'%2C%200%2C%20'y'%5D)%0Aconst%20input%20%3D%20%7Bx%3A%20%5B%7By%3A%202%2C%20z%3A%203%7D%2C%20%7By%3A%204%2C%20z%3A%205%7D%5D%7D%0A%0AR.view(lensPath%2C%20input)%20%2F%2F%20%3D%3E%202%0A%0AR.set(lensPath%2C%201%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%20%5B%7By%3A%201%2C%20z%3A%203%7D%2C%20%7By%3A%204%2C%20z%3A%205%7D%5D%7D%0A%0Aconst%20result%20%3D%20R.over(xHeadYLens%2C%20R.negate%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%20%5B%7By%3A%20-2%2C%20z%3A%203%7D%2C%20%7By%3A%204%2C%20z%3A%205%7D%5D%7D">Try this <strong>R.lensPath</strong> example in Rambda REPL</a>

lensProp

lensProp<S, K extends keyof S = keyof S>(prop: K): Lens<S, S[K]>

It returns a lens that focuses on specified property prop.

const xLens = R.lensProp('x');
const input = {x: 1, y: 2}

R.view(xLens, input) // => 1

R.set(xLens, 4, input) 
// => {x: 4, y: 2}

R.over(xLens, R.negate, input) 
// => {x: -1, y: 2}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20xLens%20%3D%20R.lensProp('x')%3B%0Aconst%20input%20%3D%20%7Bx%3A%201%2C%20y%3A%202%7D%0A%0AR.view(xLens%2C%20input)%20%2F%2F%20%3D%3E%201%0A%0AR.set(xLens%2C%204%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%204%2C%20y%3A%202%7D%0A%0Aconst%20result%20%3D%20R.over(xLens%2C%20R.negate%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%20-1%2C%20y%3A%202%7D">Try this <strong>R.lensProp</strong> example in Rambda REPL</a>

import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { prop } from './prop.js'

export function lensProp(key){
  return lens(prop(key), assoc(key))
}

import { compose } from './compose.js'
import { identity } from './identity.js'
import { inc } from './inc.js'
import { lensProp } from './lensProp.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'

const testObj = {
  a : 1,
  b : 2,
  c : 3,
}

test('focuses object the specified object property', () => {
  expect(view(lensProp('a'), testObj)).toBe(1)
})

test('returns undefined if the specified property does not exist', () => {
  expect(view(lensProp('X'), testObj)).toBeUndefined()
})

test('sets the value of the object property specified', () => {
  expect(set(
    lensProp('a'), 0, testObj
  )).toEqual({
    a : 0,
    b : 2,
    c : 3,
  })
})

test('adds the property to the object if it doesn\'t exist', () => {
  expect(set(
    lensProp('d'), 4, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  })
})

test('applies function to the value of the specified object property', () => {
  expect(over(
    lensProp('a'), inc, testObj
  )).toEqual({
    a : 2,
    b : 2,
    c : 3,
  })
})

test('applies function to undefined and adds the property if it doesn\'t exist', () => {
  expect(over(
    lensProp('X'), identity, testObj
  )).toEqual({
    a : 1,
    b : 2,
    c : 3,
    X : undefined,
  })
})

test('can be composed', () => {
  const nestedObj = {
    a : { b : 1 },
    c : 2,
  }
  const composedLens = compose(lensProp('a'), lensProp('b'))

  expect(view(composedLens, nestedObj)).toBe(1)
})

test('set s (get s) === s', () => {
  expect(set(
    lensProp('a'), view(lensProp('a'), testObj), testObj
  )).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensProp('a'), set(
    lensProp('a'), 0, testObj
  ))).toBe(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(view(lensProp('a'),
    set(
      lensProp('a'), 11, set(
        lensProp('a'), 10, testObj
      )
    ))).toBe(11)
})

lensSatisfies

lensSatisfies<PredicateInput, Input>(predicate: (x: PredicateInput) => boolean, lens: Lens<PredicateInput, Input>, input: Input): boolean

It returns true if data structure focused by the given lens satisfies the predicate.

:boom: Idea for this method comes from ramda-adjunct library

const fn = R.lensSatisfies(x => x > 5, R.lensIndex(0))
const result = [
  fn([10, 20, 30]),
  fn([1, 2, 3]),
]
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.lensSatisfies(x%20%3D%3E%20x%20%3E%205%2C%20R.lensIndex(0))%0Aconst%20result%20%3D%20%5B%0A%20%20fn(%5B10%2C%2020%2C%2030%5D)%2C%0A%20%20fn(%5B1%2C%202%2C%203%5D)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.lensSatisfies</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { view } from './view.js'

function lensSatisfiesFn(
  predicate, lens, input
){
  return Boolean(predicate(view(lens, input)))
}

export const lensSatisfies = curry(lensSatisfiesFn)

import { lensIndex } from './lensIndex.js'
import { lensPath } from './lensPath.js'
import { lensSatisfies } from './lensSatisfies.js'

const predicate = x => x > 1

test('with list', () => {
  const lens = lensIndex(0)
  const fn = lensSatisfies(predicate, lens)
  expect(fn([ 10, 20, 30 ])).toBeTrue()
  expect(fn([ 1, 2, 3 ])).toBeFalse()
})

test('with R.lensPath', () => {
  const input1 = { a : { b : 10 } }
  const input2 = { a : { b : 1 } }
  const lens = lensPath('a.b')
  const fn = lensSatisfies(predicate, lens)

  expect(fn(input1)).toBeTrue()
  expect(fn(input2)).toBeFalse()
})

lt

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.lt(2%2C%201)%2C%20R.lt(2%2C%203)%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20true%5D">Try this <strong>R.lt</strong> example in Rambda REPL</a>

lte

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.lte(2%2C%201)%2C%20R.lte(2%2C%202)%2C%20R.lte(2%2C%203)%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20true%2C%20true%5D">Try this <strong>R.lte</strong> example in Rambda REPL</a>

map

map<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>

It returns the result of looping through iterable with fn.

It works with both array and object.

:boom: Unlike Ramda's map, here property and input object are passed as arguments to fn, when iterable is an object.

const fn = x => x * 2
const fnWhenObject = (val, prop)=>{
  return `${prop}-${val}`
}

const iterable = [1, 2]
const obj = {a: 1, b: 2}

const result = [ 
  R.map(fn, iterable),
  R.map(fnWhenObject, obj)
]
// => [ [2, 4], {a: 'a-1', b: 'b-2'}]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20x%20%3D%3E%20x%20*%202%0Aconst%20fnWhenObject%20%3D%20(val%2C%20prop)%3D%3E%7B%0A%20%20return%20%60%24%7Bprop%7D-%24%7Bval%7D%60%0A%7D%0A%0Aconst%20iterable%20%3D%20%5B1%2C%202%5D%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0A%0Aconst%20result%20%3D%20%5B%20%0A%20%20R.map(fn%2C%20iterable)%2C%0A%20%20R.map(fnWhenObject%2C%20obj)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%20%5B2%2C%204%5D%2C%20%7Ba%3A%20'a-1'%2C%20b%3A%20'b-2'%7D%5D">Try this <strong>R.map</strong> example in Rambda REPL</a>

import { INCORRECT_ITERABLE_INPUT } from './_internals/constants.js'
import { isArray } from './_internals/isArray.js'
import { keys } from './_internals/keys.js'

export function mapArray(
  fn, list, isIndexed = false
){
  let index = 0
  const willReturn = Array(list.length)

  while (index < list.length){
    willReturn[ index ] = isIndexed ? fn(list[ index ], index) : fn(list[ index ])

    index++
  }

  return willReturn
}

export function mapObject(fn, obj){
  if (arguments.length === 1){
    return _obj => mapObject(fn, _obj)
  }
  let index = 0
  const objKeys = keys(obj)
  const len = objKeys.length
  const willReturn = {}

  while (index < len){
    const key = objKeys[ index ]
    willReturn[ key ] = fn(
      obj[ key ], key, obj
    )
    index++
  }

  return willReturn
}

export const mapObjIndexed = mapObject

export function map(fn, iterable){
  if (arguments.length === 1) return _iterable => map(fn, _iterable)
  if (!iterable){
    throw new Error(INCORRECT_ITERABLE_INPUT)
  }

  if (isArray(iterable)) return mapArray(fn, iterable)

  return mapObject(fn, iterable)
}

import { map as mapRamda } from 'ramda'

import { map } from './map.js'

const double = x => x * 2

describe('with array', () => {
  it('happy', () => {
    expect(map(double, [ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
  })

  it('curried', () => {
    expect(map(double)([ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
  })
})

describe('with object', () => {
  const obj = {
    a : 1,
    b : 2,
  }

  it('happy', () => {
    expect(map(double, obj)).toEqual({
      a : 2,
      b : 4,
    })
  })

  it('property as second and input object as third argument', () => {
    const obj = {
      a : 1,
      b : 2,
    }
    const iterator = (
      val, prop, inputObject
    ) => {
      expect(prop).toBeString()
      expect(inputObject).toEqual(obj)

      return val * 2
    }

    expect(map(iterator)(obj)).toEqual({
      a : 2,
      b : 4,
    })
  })
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(() => map(double, null)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"')
  expect(() => map(double)(undefined)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"')
  expect(() => mapRamda(double, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'fantasy-land/map\')"')
  expect(() =>
    mapRamda(double, undefined)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of undefined (reading \'fantasy-land/map\')"')
})

mapArray

mapArray<T>(fn: Iterator<T, T>, iterable: T[]): T[]

const result = R.mapArray(x => x + 1, [1, 2])
// => [2, 3]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mapArray(x%20%3D%3E%20x%20%2B%201%2C%20%5B1%2C%202%5D)%0A%2F%2F%20%3D%3E%20%5B2%2C%203%5D">Try this <strong>R.mapArray</strong> example in Rambda REPL</a>

mapAsync

mapAsync<T, K>(fn: AsyncIterable<T, K>, list: T[]): Promise<K[]>

Sequential asynchronous mapping with fn over members of list.

async function fn(x){
  await R.delay(1000)

  return x+1
}

const result = await R.mapAsync(fn, [1, 2, 3])
// `result` resolves after 3 seconds to `[2, 3, 4]`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?async%20function%20fn(x)%7B%0A%20%20await%20R.delay(1000)%0A%0A%20%20return%20x%2B1%0A%7D%0A%0Aconst%20result%20%3D%20await%20R.mapAsync(fn%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%60result%60%20resolves%20after%203%20seconds%20to%20%60%5B2%2C%203%2C%204%5D%60">Try this <strong>R.mapAsync</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

async function mapAsyncFn(fn, listOrObject){
  if (isArray(listOrObject)){
    const willReturn = []
    let i = 0
    for (const a of listOrObject){
      willReturn.push(await fn(a, i++))
    }

    return willReturn
  }

  const willReturn = {}
  for (const prop in listOrObject){
    willReturn[ prop ] = await fn(listOrObject[ prop ], prop)
  }

  return willReturn
}

export function mapAsync(fn, listOrObject){
  if (arguments.length === 1){
    return async _listOrObject => mapAsyncFn(fn, _listOrObject)
  }

  return new Promise((resolve, reject) => {
    mapAsyncFn(fn, listOrObject).then(resolve)
      .catch(reject)
  })
}

import { composeAsync } from './composeAsync.js'
import { delay } from './delay.js'
import { map } from './map.js'
import { mapAsync } from './mapAsync.js'

const rejectDelay = a =>
  new Promise((_, reject) => {
    setTimeout(() => {
      reject(a + 20)
    }, 100)
  })

test('happy', async () => {
  const fn = async (x, prop) => {
    await delay(100)
    expect(prop).toBeNumber()

    return x + 1
  }
  const result = await mapAsync(fn, [ 1, 2, 3 ])
  expect(result).toEqual([ 2, 3, 4 ])
})

test('with object', async () => {
  const fn = async (x, prop) => {
    expect(prop).toBeString()

    return x + 1
  }
  const result = await mapAsync(fn, {
    a : 1,
    b : 2,
  })
  expect(result).toEqual({
    a : 2,
    b : 3,
  })
})

test('with R.composeAsync', async () => {
  const result = await composeAsync(
    map(x => x + 1),
    mapAsync(async x => {
      delay(x)

      return x
    }),
    map(x => x * 10)
  )([ 1, 2, 3 ])
  expect(result).toEqual([ 11, 21, 31 ])
})

test('error', async () => {
  try {
    await mapAsync(rejectDelay)([ 1, 2, 3 ])
  } catch (err){
    expect(err).toBe(21)
  }
})

mapcat

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mapcat()%0A%2F%2F%20%3D%3E">Try this <strong>R.mapcat</strong> example in Rambda REPL</a>

mapIndexed

Same as R.map, but it passes index as second argument to the iterator, when looping over arrays.

mapKeys

mapKeys<T, U>(changeKeyFn: (x: string) => string, obj: { [key: string]: T}): U

It takes an object and returns a new object with changed keys according to changeKeyFn function.

const obj = {a: 1, b: 2}
const changeKeyFn = prop => `{prop}_foo`
const result = R.mapKeys(changeKeyFn, Record<string, unknown>)
// => {a_foo: 1, b_foo: 2}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0Aconst%20changeKeyFn%20%3D%20prop%20%3D%3E%20%60%7Bprop%7D_foo%60%0Aconst%20result%20%3D%20R.mapKeys(changeKeyFn%2C%20Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20%7Ba_foo%3A%201%2C%20b_foo%3A%202%7D">Try this <strong>R.mapKeys</strong> example in Rambda REPL</a>

export function mapKeys(changeKeyFn, obj){
  if (arguments.length === 1) return _obj => mapKeys(changeKeyFn, _obj)
  const toReturn = {}

  Object.keys(obj).forEach(prop => toReturn[ changeKeyFn(prop) ] = obj[ prop ])

  return toReturn
}

import { mapKeys } from './mapKeys.js'

const obj = {
  a : 1,
  b : 2,
}
const changeKeyFn = prop => `${ prop }_foo`
const expected = {
  a_foo : 1,
  b_foo : 2,
}

test('happy', () => {
  const result = mapKeys(changeKeyFn, obj)

  expect(result).toEqual(expected)
})

test('curried', () => {
  const result = mapKeys(changeKeyFn)(obj)

  expect(result).toEqual(expected)
})

mapObject

mapObject<T>(fn: ObjectIterator<T, T>, iterable: Dictionary<T>): Dictionary<T>

const result = R.mapObject(x => x + 1, {a:1, b:2})
// => {a:2, b:3}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mapObject(x%20%3D%3E%20x%20%2B%201%2C%20%7Ba%3A1%2C%20b%3A2%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A2%2C%20b%3A3%7D">Try this <strong>R.mapObject</strong> example in Rambda REPL</a>

mapObjIndexed

It works the same way as R.map does for objects. It is added as Ramda also has this method.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(val%2C%20prop)%20%3D%3E%20%7B%0A%20%20return%20%60%24%7Bprop%7D-%24%7Bval%7D%60%0A%7D%0A%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0A%0Aconst%20result%20%3D%20R.mapObjIndexed(fn%2C%20obj)%0A%2F%2F%20%3D%3E%20%7Ba%3A%20'a-1'%2C%20b%3A%20'b-2'%7D">Try this <strong>R.mapObjIndexed</strong> example in Rambda REPL</a>

mapParallelAsync

mapParallelAsync<T, K>(fn: AsyncIterable<T, K>, list: T[]): Promise<K[]>

Parallel asynchronous mapping with fn over members of list.

async function fn(x){
  await R.delay(1000)

  return x+1
}

const result = await R.mapParallelAsync(fn, [1, 2, 3])
// `result` resolves after 1 second to `[2, 3, 4]`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?async%20function%20fn(x)%7B%0A%20%20await%20R.delay(1000)%0A%0A%20%20return%20x%2B1%0A%7D%0A%0Aconst%20result%20%3D%20await%20R.mapParallelAsync(fn%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%60result%60%20resolves%20after%201%20second%20to%20%60%5B2%2C%203%2C%204%5D%60">Try this <strong>R.mapParallelAsync</strong> example in Rambda REPL</a>

export async function mapParallelAsyncFn(fn, arr){
  const promised = arr.map((a, i) => fn(a, i))

  return Promise.all(promised)
}

export function mapParallelAsync(fn, arr){
  if (arguments.length === 1){
    return async holder => mapParallelAsyncFn(fn, holder)
  }

  return new Promise((resolve, reject) => {
    mapParallelAsyncFn(fn, arr).then(resolve)
      .catch(reject)
  })
}

import { willFailAssertion } from './_internals/testUtils.js'
import { composeAsync } from './composeAsync.js'
import { delay } from './delay.js'
import { map } from './map.js'
import { mapParallelAsync } from './mapParallelAsync.js'

test('happy', async () => {
  const fn = async x => {
    await delay(100)

    return x + 10
  }
  const result = await mapParallelAsync(fn, [ 1, 2, 3 ])
  expect(result).toEqual([ 11, 12, 13 ])
})

test('composeAsync', async () => {
  const result = await composeAsync(
    mapParallelAsync(async x => {
      await delay(100)

      return x + 1
    }),
    mapParallelAsync(async x => {
      await delay(100)

      return x + 10
    }),
    map(x => x * 10)
  )([ 1, 2, 3 ])
  expect(result).toEqual([ 21, 31, 41 ])
})

test('error', async () => {
  try {
    const fn = async () => {
      JSON.parse('{:')
    }
    await mapParallelAsync(fn, [ 1, 2, 3 ])
    willFailAssertion()
  } catch (err){
    expect(err.message).toBeTruthy()
  }
})

test('pass index as second argument', async () => {
  await mapParallelAsync((x, i) => {
    expect(x % 10).toBe(0)
    expect(typeof i).toBe('number')
  },
  [ 10, 20, 30 ])
})

mapParallelAsyncWithLimit

mapParallelAsyncWithLimit<T, K>(fn: AsyncIterable<T, K>, limit: number, list: T[]): Promise<K[]>

It is similar to R.mapParallelAsync in that it uses Promise.all, but not over the whole list, rather than with only slice from list with length limit.

:boom: For example usage, please check R.mapAsyncLimit tests.

import { mapParallelAsync, mapParallelAsyncFn } from './mapParallelAsync.js'
import { splitEvery } from './splitEvery.js'

async function mapParallelAsyncWithLimitFn(
  iterable, limit, list
){
  if (list.length < limit) return mapParallelAsync(iterable, list)

  const slices = splitEvery(limit, list)

  let toReturn = []
  for (const slice of slices){
    const iterableResult = await mapParallelAsyncFn(iterable, slice)
    toReturn = [ ...toReturn, ...iterableResult ]
  }

  return toReturn
}

export function mapParallelAsyncWithLimit(
  iterable, limit, list
){
  if (arguments.length === 2){
    return async _list => mapParallelAsyncWithLimitFn(
      iterable, limit, _list
    )
  }

  return new Promise((resolve, reject) => {
    mapParallelAsyncWithLimitFn(
      iterable, limit, list
    )
      .then(resolve)
      .catch(reject)
  })
}

import isCI from 'is-ci'

import { composeAsync } from './composeAsync.js'
import { delay } from './delay.js'
import { mapAsync } from './mapAsync.js'
import { mapParallelAsyncWithLimit } from './mapParallelAsyncWithLimit.js'
import { toDecimal } from './toDecimal.js'

jest.setTimeout(30000)

test('happy', async () => {
  const limit = 3
  const startTime = new Date().getTime()
  const list = [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
  const iterable = async x => {
    await delay(500)

    return x + 1
  }
  const result = await mapParallelAsyncWithLimit(
    iterable, limit, list
  )
  const endTime = new Date().getTime()
  const diffTime = endTime - startTime

  const startTime2 = new Date().getTime()
  await mapAsync(iterable, list)
  const endTime2 = new Date().getTime()
  const diffTime2 = endTime2 - startTime2

  const methodScale = toDecimal((diffTime2 - diffTime) / 1000, 0)
  expect(result).toEqual([ 2, 3, 4, 5, 6, 7, 8, 9, 10 ])
  if (!isCI) expect(methodScale).toBe(limit)
})

const fn = async x => {
  await delay(100)

  return x + 1
}

test('with R.composeAsync', async () => {
  const result = await composeAsync(mapParallelAsyncWithLimit(fn, 2), x =>
    x.map(xx => xx + 1))([ 1, 2, 3, 4, 5, 6 ])
  expect(result).toEqual([ 3, 4, 5, 6, 7, 8 ])
})

test('fallback to R.mapFastAsync', async () => {
  const result = await mapParallelAsyncWithLimit(
    fn, 4, [ 1, 2, 3 ]
  )
  expect(result).toEqual([ 2, 3, 4 ])
})

mapToObject

mapToObject<T, U extends object>(fn: (input: T) => U|false, list: readonly T[]): U

This method allows to generate an object from a list using input function fn.

This function must return either an object or false for every member of list input.

If false is returned, then this element of list will be skipped in the calculation of the result.

All of returned objects will be merged to generate the final result.

const list = [1, 2, 3, 12]
const fn = x => {
  if(x > 10) return false
  return x % 2 ? {[x]: x + 1}: {[x]: x + 10}
}

const result = mapToObject(fn, list)
const expected = {'1': 2, '2': 12, '3': 4}
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%2012%5D%0Aconst%20fn%20%3D%20x%20%3D%3E%20%7B%0A%20%20if(x%20%3E%2010)%20return%20false%0A%20%20return%20x%20%25%202%20%3F%20%7B%5Bx%5D%3A%20x%20%2B%201%7D%3A%20%7B%5Bx%5D%3A%20x%20%2B%2010%7D%0A%7D%0A%0Aconst%20result%20%3D%20mapToObject(fn%2C%20list)%0Aconst%20expected%20%3D%20%7B'1'%3A%202%2C%20'2'%3A%2012%2C%20'3'%3A%204%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.mapToObject</strong> example in Rambda REPL</a>

import { map } from './map.js'
import { mergeAll } from './mergeAll.js'
import { ok } from './ok.js'
import { type } from './type.js'

export function mapToObject(fn, list){
  if (arguments.length === 1){
    return listHolder => mapToObject(fn, listHolder)
  }
  ok(type(fn), type(list))('Function', 'Array')

  return mergeAll(map(fn, list))
}

import { mapToObject } from './mapToObject.js'

const list = [ 1, 2, 3 ]
const fn = x => x % 2 ? { [ x ] : x + 1 } : { [ x ] : x + 10 }
const expected = {
  1 : 2,
  2 : 12,
  3 : 4,
}

test('happy', () => {
  const result = mapToObject(fn, list)
  expect(result).toEqual(expected)
})

test('curried', () => {
  const result = mapToObject(fn)(list)
  expect(result).toEqual(expected)
})

test('string.fn test', () => {
  const list = [ 'auto', 'bar=false', 'foo', 'baz=1.5', 's=more', 'k=2' ]
  const fn = x => {
    const [ key, value ] = x.split('=')
    if (value === undefined || value === 'true'){
      return { [ key ] : true }
    }
    if (value === 'false'){
      return { [ key ] : false }
    }

    if (Number.isNaN(Number(value))){
      return { [ key ] : value }
    }

    return { [ key ] : Number(value) }
  }

  const expectedResult = {
    auto : true,
    foo  : true,
    bar  : false,
    baz  : 1.5,
    s    : 'more',
    k    : 2,
  }
  const result = mapToObject(fn, list)

  expect(result).toEqual(expectedResult)
})

test('bad path', () => {
  expect(() => mapToObject(1, null)).toThrowErrorMatchingInlineSnapshot(`
    "Failed R.ok -
    reason: {"input":"Number","schema":"Function"}
    all inputs: ["Number","Null"]
    all schemas: ["Function","Array"]"
  `)
})

mapToObjectAsync

mapToObjectAsync<T, U extends object>(fn: (input: T) => Promise<U|false>, list: readonly T[]): Promise<U>

Asynchronous version of R.mapToObject

import { mapAsync } from './mapAsync.js'

export async function mapToObjectAsyncFn(fn, list){
  let toReturn = {}

  const innerIterable = async x => {
    const intermediateResult = await fn(x)
    if (intermediateResult === false) return
    toReturn = {
      ...toReturn,
      ...intermediateResult,
    }
  }

  await mapAsync(innerIterable, list)

  return toReturn
}

export function mapToObjectAsync(fn, list){
  if (arguments.length === 1){
    return async _list => mapToObjectAsyncFn(fn, _list)
  }

  return new Promise((resolve, reject) => {
    mapToObjectAsyncFn(fn, list).then(resolve)
      .catch(reject)
  })
}

import { composeAsync } from './composeAsync.js'
import { delay } from './delay.js'
import { mapToObjectAsync } from './mapToObjectAsync.js'

const list = [ 1, 2, 3, 12 ]
const fn = async x => {
  await delay(100)
  if (x > 10) return false

  return x % 2 ? { [ `key${ x }` ] : x + 1 } : { [ `key${ x }` ] : x + 10 }
}

const expected = {
  key1 : 2,
  key2 : 12,
  key3 : 4,
}

test('happy', async () => {
  const result = await mapToObjectAsync(fn, list)
  expect(result).toEqual(expected)
})

test('with R.composeAsync', async () => {
  const result = await composeAsync(mapToObjectAsync(fn), x =>
    x.filter(xx => xx > 1))(list)

  expect(result).toEqual({
    key2 : 12,
    key3 : 4,
  })
})

match

match(regExpression: RegExp, str: string): string[]

Curried version of String.prototype.match which returns empty array, when there is no match.

const result = [
  R.match('a', 'foo'),
  R.match(/([a-z]a)/g, 'bananas')
]
// => [[], ['ba', 'na', 'na']]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.match('a'%2C%20'foo')%2C%0A%20%20R.match(%2F(%5Ba-z%5Da)%2Fg%2C%20'bananas')%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B%5D%2C%20%5B'ba'%2C%20'na'%2C%20'na'%5D%5D">Try this <strong>R.match</strong> example in Rambda REPL</a>

export function match(pattern, input){
  if (arguments.length === 1) return _input => match(pattern, _input)

  const willReturn = input.match(pattern)

  return willReturn === null ? [] : willReturn
}

import { equals } from './equals.js'
import { match } from './match.js'

test('happy', () => {
  expect(match(/a./g)('foo bar baz')).toEqual([ 'ar', 'az' ])
})

test('fallback', () => {
  expect(match(/a./g)('foo')).toEqual([])
})

test('with string', () => {
  expect(match('a', 'foo')).toEqual([])
  expect(equals(match('o', 'foo'), [ 'o' ])).toBeTrue()
})

test('throwing', () => {
  expect(() => {
    match(/a./g, null)
  }).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'match\')"')
})

mathMod

R.mathMod behaves like the modulo operator should mathematically, unlike the % operator (and by extension, R.modulo). So while -17 % 5 is -2, mathMod(-17, 5) is 3.

:boom: Explanation is taken from Ramda documentation site.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.mathMod(-17%2C%205)%2C%0A%20%20R.mathMod(17%2C%205)%2C%0A%20%20R.mathMod(17%2C%20-5)%2C%20%20%0A%20%20R.mathMod(17%2C%200)%20%20%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B3%2C%202%2C%20NaN%2C%20NaN%5D">Try this <strong>R.mathMod</strong> example in Rambda REPL</a>

max

It returns the greater value between x and y.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.max(5%2C%207)%2C%20%20%0A%20%20R.max('bar'%2C%20'foo')%2C%20%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B7%2C%20'foo'%5D">Try this <strong>R.max</strong> example in Rambda REPL</a>

maxBy

It returns the greater value between x and y according to compareFn function.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20compareFn%20%3D%20Math.abs%0A%0Aconst%20result%20%3D%20R.maxBy(compareFn%2C%205%2C%20-7)%20%2F%2F%20%3D%3E%20-7">Try this <strong>R.maxBy</strong> example in Rambda REPL</a>

maybe

maybe<T>(ifRule: boolean, whenIf: T | Func<T>, whenElse: T | Func<T>): T

It acts as ternary operator and it is helpful when we have nested ternaries.

All of the inputs can be either direct values or anonymous functions. This is helpful if we don't want to evaluate certain paths as we can wrap this logic in a function.

const x = 4
const y = 8

const ifRule = x > 2
const whenIf = y > 10 ? 3 : 7
const whenElse = () => {
  // just to show that it won't be evaluated
  return JSON.parse('{a:')
}

const result = R.maybe(
  ifRule,
  whenIf,
  whenElse,
)
// `result` is `7`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%204%0Aconst%20y%20%3D%208%0A%0Aconst%20ifRule%20%3D%20x%20%3E%202%0Aconst%20whenIf%20%3D%20y%20%3E%2010%20%3F%203%20%3A%207%0Aconst%20whenElse%20%3D%20()%20%3D%3E%20%7B%0A%20%20%2F%2F%20just%20to%20show%20that%20it%20won't%20be%20evaluated%0A%20%20return%20JSON.parse('%7Ba%3A')%0A%7D%0A%0Aconst%20result%20%3D%20R.maybe(%0A%20%20ifRule%2C%0A%20%20whenIf%2C%0A%20%20whenElse%2C%0A)%0A%2F%2F%20%60result%60%20is%20%607%60">Try this <strong>R.maybe</strong> example in Rambda REPL</a>

import { type } from './type.js'

export function maybe(
  ifRule, whenIf, whenElse
){
  const whenIfInput =
    ifRule && type(whenIf) === 'Function' ? whenIf() : whenIf

  const whenElseInput =
    !ifRule && type(whenElse) === 'Function' ? whenElse() : whenElse

  return ifRule ? whenIfInput : whenElseInput
}

import { maybe } from './maybe.js'

const WHEN_IF = 'WHEN_IF'
const WHEN_ELSE = 'WHEN_ELSE'

test('prevent type error', () => {
  const x = 5
  const y = null
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, () => y.a === 'foo'
  )

  expect(result).toBe(WHEN_IF)
})

test('whenElse is a function', () => {
  const x = 2
  const y = { a : 1 }
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, () => y.a === 'foo'
  )

  expect(result).toBeFalse()
})

test('whenIf', () => {
  const x = 5
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, WHEN_ELSE
  )

  expect(result).toBe(WHEN_IF)
})

test('whenIf is a function', () => {
  const x = 5
  const ifRule = () => x > 3

  const result = maybe(
    ifRule, () => WHEN_IF, WHEN_ELSE
  )

  expect(result).toBe(WHEN_IF)
})

test('whenElse', () => {
  const x = 1
  const ifRule = x > 3

  const result = maybe(
    ifRule, WHEN_IF, WHEN_ELSE
  )

  expect(result).toBe(WHEN_ELSE)
})

mean

mean(list: number[]): number

It returns the mean value of list input.

R.mean([ 2, 7 ])
// => 4.5

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mean(%5B%202%2C%207%20%5D)%0A%2F%2F%20%3D%3E%204.5">Try this <strong>R.mean</strong> example in Rambda REPL</a>

import { sum } from './sum.js'

export function mean(list){
  return sum(list) / list.length
}

import { mean } from './mean.js'

test('happy', () => {
  expect(mean([ 2, 7 ])).toBe(4.5)
})

test('with NaN', () => {
  expect(mean([])).toBeNaN()
})

median

median(list: number[]): number

It returns the median value of list input.

R.median([ 7, 2, 10, 9 ]) // => 8

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.median(%5B%207%2C%202%2C%2010%2C%209%20%5D)%20%2F%2F%20%3D%3E%208">Try this <strong>R.median</strong> example in Rambda REPL</a>

import { mean } from './mean.js'

export function median(list){
  const len = list.length
  if (len === 0) return NaN
  const width = 2 - len % 2
  const idx = (len - width) / 2

  return mean(Array.prototype.slice
    .call(list, 0)
    .sort((a, b) => {
      if (a === b) return 0

      return a < b ? -1 : 1
    })
    .slice(idx, idx + width))
}

import { median } from './median.js'

test('happy', () => {
  expect(median([ 2 ])).toBe(2)
  expect(median([ 7, 2, 10, 2, 9 ])).toBe(7)
})

test('with empty array', () => {
  expect(median([])).toBeNaN()
})

memoize

When fn is called for a second time with the same input, then the cache result is returned instead of calling again fn.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?let%20result%20%3D%200%0Aconst%20fn%20%3D%20(a%2Cb)%20%3D%3E%7B%0A%20%20result%2B%2B%0A%0A%20%20return%20a%20%2B%20b%0A%7D%0Aconst%20memoized%20%3D%20R.memoize(fn)%0Amemoized(1%2C%202)%0Amemoized(1%2C%202)%0Aconst%20result%20%3D%20%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%601%60">Try this <strong>R.memoize</strong> example in Rambda REPL</a>

memoizeWith

Creates a new function that, when invoked, caches the result of calling fn for a given argument set and returns the result.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20keyGen%20%3D%20(a%2Cb)%20%3D%3E%20a%20%2B%20b%0Alet%20result%20%3D%200%0Aconst%20fn%20%3D%20(a%2Cb)%20%3D%3E%7B%0A%20%20result%2B%2B%0A%0A%20%20return%20a%20%2B%20b%0A%7D%0Aconst%20memoized%20%3D%20R.memoizeWith(keyGen%2C%20fn)%0Amemoized(1%2C%202)%0Amemoized(1%2C%202)%0Aconst%20result%20%3D%20%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%601%60">Try this <strong>R.memoizeWith</strong> example in Rambda REPL</a>

merge

Same as R.mergeRight.

mergeAll

mergeAll<T>(list: object[]): T

It merges all objects of list array sequentially and returns the result.

const list = [
  {a: 1},
  {b: 2},
  {c: 3}
]
const result = R.mergeAll(list)
const expected = {
  a: 1,
  b: 2,
  c: 3
}
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%201%7D%2C%0A%20%20%7Bb%3A%202%7D%2C%0A%20%20%7Bc%3A%203%7D%0A%5D%0Aconst%20result%20%3D%20R.mergeAll(list)%0Aconst%20expected%20%3D%20%7B%0A%20%20a%3A%201%2C%0A%20%20b%3A%202%2C%0A%20%20c%3A%203%0A%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.mergeAll</strong> example in Rambda REPL</a>

import { map } from './map.js'
import { mergeRight } from './mergeRight.js'

export function mergeAll(arr){
  let willReturn = {}
  map(val => {
    willReturn = mergeRight(willReturn, val)
  }, arr)

  return willReturn
}

import { mergeAll } from './mergeAll.js'

test('case 1', () => {
  const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]
  const expectedResult = {
    a : 1,
    b : 2,
    c : 3,
  }
  expect(mergeAll(arr)).toEqual(expectedResult)
})

test('case 2', () => {
  expect(mergeAll([ { foo : 1 }, { bar : 2 }, { baz : 3 } ])).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

describe('acts as if nil values are simply empty objects', () => {
  it('if the first object is nil', () => {
    expect(mergeAll([ null, { foo : 1 }, { foo : 2 }, { bar : 2 } ])).toEqual({
      foo : 2,
      bar : 2,
    })
  })

  it('if the last object is nil', () => {
    expect(mergeAll([ { foo : 1 }, { foo : 2 }, { bar : 2 }, undefined ])).toEqual({
      foo : 2,
      bar : 2,
    })
  })

  it('if an intermediate object is nil', () => {
    expect(mergeAll([ { foo : 1 }, { foo : 2 }, null, { bar : 2 } ])).toEqual({
      foo : 2,
      bar : 2,
    })
  })
})

mergeDeepLeft

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mergeDeepLeft(%0A%20%20%7Ba%3A%20%7Bb%3A%201%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%202%2C%20c%3A%203%7D%7D%0A)%0A%2F%2F%20%3D%3E%20%7Ba%3A%20%7Bb%3A%201%2C%20c%3A%203%7D%7D">Try this <strong>R.mergeDeepLeft</strong> example in Rambda REPL</a>

mergeDeepRight

mergeDeepRight<Output>(target: object, newProps: object): Output

Creates a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:

• and both values are objects, the two values will be recursively merged
• otherwise the value from the second object will be used.

import { clone } from './clone.js'
import { type } from './type.js'

export function mergeDeepRight(target, source){
  if (arguments.length === 1){
    return sourceHolder => mergeDeepRight(target, sourceHolder)
  }

  const willReturn = clone(target)

  Object.keys(source).forEach(key => {
    if (type(source[ key ]) === 'Object'){
      if (type(target[ key ]) === 'Object'){
        willReturn[ key ] = mergeDeepRight(target[ key ], source[ key ])
      } else {
        willReturn[ key ] = source[ key ]
      }
    } else {
      willReturn[ key ] = source[ key ]
    }
  })

  return willReturn
}

import { mergeDeepRight } from './mergeDeepRight.js'

const student = {
  name    : 'foo',
  age     : 10,
  contact : {
    a     : 1,
    email : 'foo@example.com',
  },
}
const teacher = {
  age     : 40,
  contact : { email : 'baz@example.com' },
  songs   : { title : 'Remains the same' },
}

test('when merging object with lists inside them', () => {
  const a = {
    a : [ 1, 2, 3 ],
    b : [ 4, 5, 6 ],
  }
  const b = {
    a : [ 7, 8, 9 ],
    b : [ 10, 11, 12 ],
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    a : [ 7, 8, 9 ],
    b : [ 10, 11, 12 ],
  }
  expect(result).toEqual(expected)
})

test('happy', () => {
  const result = mergeDeepRight(student, teacher)
  const curryResult = mergeDeepRight(student)(teacher)
  const expected = {
    age     : 40,
    name    : 'foo',
    contact : {
      a     : 1,
      email : 'baz@example.com',
    },
    songs : { title : 'Remains the same' },
  }

  expect(result).toEqual(expected)
  expect(curryResult).toEqual(expected)
})

test('issue 650', () => {
  expect(Object.keys(mergeDeepRight({ a : () => {} }, { b : () => {} }))).toEqual([
    'a',
    'b',
  ])
})

test('ramda compatible test 1', () => {
  const a = {
    w : 1,
    x : 2,
    y : { z : 3 },
  }
  const b = {
    a : 4,
    b : 5,
    c : { d : 6 },
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    w : 1,
    x : 2,
    y : { z : 3 },
    a : 4,
    b : 5,
    c : { d : 6 },
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 2', () => {
  const a = {
    a : {
      b : 1,
      c : 2,
    },
    y : 0,
  }
  const b = {
    a : {
      b : 3,
      d : 4,
    },
    z : 0,
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    a : {
      b : 3,
      c : 2,
      d : 4,
    },
    y : 0,
    z : 0,
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 3', () => {
  const a = {
    w : 1,
    x : { y : 2 },
  }
  const result = mergeDeepRight(a, { x : { y : 3 } })
  const expected = {
    w : 1,
    x : { y : 3 },
  }
  expect(result).toEqual(expected)
})

test('functions are not discarded', () => {
  const obj = { foo : () => {} }
  expect(typeof mergeDeepRight(obj, {}).foo).toBe('function')
})

mergeLeft

mergeLeft<Output>(newProps: object, target: object): Output

Same as R.merge, but in opposite direction.

const result = R.mergeLeft(
  {a: 10},
  {a: 1, b: 2}
)
// => {a:10, b: 2}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mergeLeft(%0A%20%20%7Ba%3A%2010%7D%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%202%7D%0A)%0A%2F%2F%20%3D%3E%20%7Ba%3A10%2C%20b%3A%202%7D">Try this <strong>R.mergeLeft</strong> example in Rambda REPL</a>

import { mergeRight } from './mergeRight.js'

export function mergeLeft(x, y){
  if (arguments.length === 1) return _y => mergeLeft(x, _y)

  return mergeRight(y, x)
}

import { mergeLeft } from './mergeLeft.js'

const obj = {
  foo : 1,
  bar : 2,
}

test('happy', () => {
  expect(mergeLeft({ bar : 20 }, obj)).toEqual({
    foo : 1,
    bar : 20,
  })
})

test('curry', () => {
  expect(mergeLeft({ baz : 3 })(obj)).toEqual({
    foo : 1,
    bar : 2,
    baz : 3,
  })
})

test('when undefined or null instead of object', () => {
  expect(mergeLeft(null, undefined)).toEqual({})
  expect(mergeLeft(obj, null)).toEqual(obj)
  expect(mergeLeft(obj, undefined)).toEqual(obj)
  expect(mergeLeft(undefined, obj)).toEqual(obj)
})

mergeRight

It creates a copy of target object with overwritten newProps properties. Previously known as R.merge but renamed after Ramda did the same.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20target%20%3D%20%7B%20'foo'%3A%200%2C%20'bar'%3A%201%20%7D%0Aconst%20newProps%20%3D%20%7B%20'foo'%3A%207%20%7D%0A%0Aconst%20result%20%3D%20R.mergeRight(target%2C%20newProps)%0A%2F%2F%20%3D%3E%20%7B%20'foo'%3A%207%2C%20'bar'%3A%201%20%7D">Try this <strong>R.mergeRight</strong> example in Rambda REPL</a>

mergeWith

mergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Record<string, unknown>

It takes two objects and a function, which will be used when there is an overlap between the keys.

const result = R.mergeWith(
  R.concat,
  {values : [ 10, 20 ]},
  {values : [ 15, 35 ]}
)
// => [ 10, 20, 15, 35 ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mergeWith(%0A%20%20R.concat%2C%0A%20%20%7Bvalues%20%3A%20%5B%2010%2C%2020%20%5D%7D%2C%0A%20%20%7Bvalues%20%3A%20%5B%2015%2C%2035%20%5D%7D%0A)%0A%2F%2F%20%3D%3E%20%5B%2010%2C%2020%2C%2015%2C%2035%20%5D">Try this <strong>R.mergeWith</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

export function mergeWithFn(
  mergeFn, aInput, bInput
){
  const a = aInput ?? {}
  const b = bInput ?? {}
  const willReturn = {}

  Object.keys(a).forEach(key => {
    if (b[ key ] === undefined) willReturn[ key ] = a[ key ]
    else willReturn[ key ] = mergeFn(a[ key ], b[ key ])
  })

  Object.keys(b).forEach(key => {
    if (willReturn[ key ] !== undefined) return

    if (a[ key ] === undefined) willReturn[ key ] = b[ key ]
    else willReturn[ key ] = mergeFn(a[ key ], b[ key ])
  })

  return willReturn
}

export const mergeWith = curry(mergeWithFn)

import { concat } from './concat.js'
import { mergeWithFn } from './mergeWith.js'

test('happy', () => {
  const result = mergeWithFn(
    concat,
    {
      a      : true,
      values : [ 10, 20 ],
    },
    {
      b      : true,
      values : [ 15, 35 ],
    }
  )
  const expected = {
    a      : true,
    b      : true,
    values : [ 10, 20, 15, 35 ],
  }
  expect(result).toEqual(expected)
})

// https://github.com/ramda/ramda/pull/3222/files#diff-d925d9188b478d2f1d4b26012c6dddac374f9e9d7a336604d654b9a113bfc857
describe('acts as if nil values are simply empty objects', () => {
  it('if the first object is nil and the second empty', () => {
    expect(mergeWithFn(
      concat, undefined, {}
    )).toEqual({})
  })

  it('if the first object is empty and the second nil', () => {
    expect(mergeWithFn(
      concat, {}, null
    )).toEqual({})
  })

  it('if both objects are nil', () => {
    expect(mergeWithFn(
      concat, undefined, null
    )).toEqual({})
  })

  it('if the first object is not empty and the second is nil', () => {
    expect(mergeWithFn(
      concat, { a : 'a' }, null
    )).toEqual({ a : 'a' })
  })

  it('if the first object is nil and the second is not empty', () => {
    expect(mergeWithFn(
      concat, undefined, { a : 'a' }
    )).toEqual({ a : 'a' })
  })
})

min

It returns the lesser value between x and y.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.min(5%2C%207)%2C%20%20%0A%20%20R.min('bar'%2C%20'foo')%2C%20%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B5%2C%20'bar'%5D">Try this <strong>R.min</strong> example in Rambda REPL</a>

minBy

It returns the lesser value between x and y according to compareFn function.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20compareFn%20%3D%20Math.abs%0A%0Aconst%20result%20%3D%20R.minBy(compareFn%2C%20-5%2C%202)%20%2F%2F%20%3D%3E%20-5">Try this <strong>R.minBy</strong> example in Rambda REPL</a>

modify

modify<K extends PropertyKey, T>(prop: K, fn: (value: T) => T): <U extends Record<K, T>>(object: U) => U

const result = R.modify()
// =>

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.modify()%0A%2F%2F%20%3D%3E">Try this <strong>R.modify</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { isIterable } from './_internals/isIterable.js'
import { curry } from './curry.js'
import { updateFn } from './update.js'

function modifyFn(
  property, fn, iterable
){
  if (!isIterable(iterable)) return iterable
  if (iterable[ property ] === undefined) return iterable
  if (isArray(iterable)){
    return updateFn(
      property, fn(iterable[ property ]), iterable
    )
  }

  return {
    ...iterable,
    [ property ] : fn(iterable[ property ]),
  }
}

export const modify = curry(modifyFn)

import { modify as modifyRamda } from 'ramda'

import { compareCombinations, FALSY_VALUES } from './_internals/testUtils.js'
import { add } from './add.js'
import { compose } from './compose.js'
import { modify } from './modify.js'

const person = {
  name : 'foo',
  age  : 20,
}

test('happy', () => {
  expect(modify(
    'age', x => x + 1, person
  )).toEqual({
    name : 'foo',
    age  : 21,
  })
})

test('property is missing', () => {
  expect(modify(
    'foo', x => x + 1, person
  )).toEqual(person)
})

test('adjust if `array` at the given key with the `transformation` function', () => {
  expect(modify(
    1, add(1), [ 100, 1400 ]
  )).toEqual([ 100, 1401 ])
})

describe('ignores transformations if the input value is not Array and Object', () => {
  ;[ 42, undefined, null, '' ].forEach(value => {
    it(`${ value }`, () => {
      expect(modify(
        'a', add(1), value
      )).toEqual(value)
    })
  })
})

const possibleProperties = [ ...FALSY_VALUES, 'foo', 0 ]
const possibleTransformers = [
  ...FALSY_VALUES,
  add(1),
  add('foo'),
  compose,
  String,
]
const possibleObjects = [
  ...FALSY_VALUES,
  {},
  [ 1, 2, 3 ],
  {
    a   : 1,
    foo : 2,
  },
  {
    a   : 1,
    foo : [ 1 ],
  },
  {
    a   : 1,
    foo : 'bar',
  },
]

describe('brute force', () => {
  compareCombinations({
    fn          : modify,
    fnRamda     : modifyRamda,
    firstInput  : possibleProperties,
    secondInput : possibleTransformers,
    thirdInput  : possibleObjects,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 630,
        }
      `)
    },
  })
})

modifyPath

It changes a property of object on the base of provided path and transformer function.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.modifyPath('a.b.c'%2C%20x%3D%3E%20x%2B1%2C%20%7Ba%3A%7Bb%3A%20%7Bc%3A1%7D%7D%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%7Bb%3A%20%7Bc%3A2%7D%7D%7D">Try this <strong>R.modifyPath</strong> example in Rambda REPL</a>

modulo

Curried version of x%y.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.modulo(17%2C%203)%20%2F%2F%20%3D%3E%202">Try this <strong>R.modulo</strong> example in Rambda REPL</a>

move

It returns a copy of list with exchanged fromIndex and toIndex elements.

:boom: Rambda.move doesn't support negative indexes - it throws an error.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20result%20%3D%20R.move(0%2C%201%2C%20list)%0A%2F%2F%20%3D%3E%20%5B2%2C%201%2C%203%5D">Try this <strong>R.move</strong> example in Rambda REPL</a>

multiply

Curried version of x*y.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.multiply(2%2C%204)%20%2F%2F%20%3D%3E%208">Try this <strong>R.multiply</strong> example in Rambda REPL</a>

negate

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.negate(420)%2F%2F%20%3D%3E%20-420">Try this <strong>R.negate</strong> example in Rambda REPL</a>

nextIndex

nextIndex(index: number, list: any[]): number

It returns the next index of the list.

If we have reached the end of the list, then it will return 0.

const list = [1, 2, 3]

const result = [
  R.nextIndex(0, list),
  R.nextIndex(1, list),
  R.nextIndex(2, list),
  R.nextIndex(10, list)
]
// => [1, 2, 0, 0]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.nextIndex(0%2C%20list)%2C%0A%20%20R.nextIndex(1%2C%20list)%2C%0A%20%20R.nextIndex(2%2C%20list)%2C%0A%20%20R.nextIndex(10%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%200%2C%200%5D">Try this <strong>R.nextIndex</strong> example in Rambda REPL</a>

export function nextIndex(index, list){
  return index >= list.length - 1 ? 0 : index + 1
}

import { nextIndex } from './nextIndex.js'

const list = [ 1, 2, 3, 4 ]

test('happy path', () => {
  expect(nextIndex(2, list)).toBe(3)
})

test('go back to the start', () => {
  expect(nextIndex(3, list)).toBe(0)
})

test('current index is too big', () => {
  expect(nextIndex(32, list)).toBe(0)
})

none

none<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if all members of array list returns false, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > 6

const result = R.none(predicate, arr)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%200%2C%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%206%0A%0Aconst%20result%20%3D%20R.none(predicate%2C%20arr)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.none</strong> example in Rambda REPL</a>

export function none(predicate, list){
  if (arguments.length === 1) return _list => none(predicate, _list)

  for (let i = 0; i < list.length; i++){
    if (predicate(list[ i ])) return false
  }

  return true
}

import { none } from './none.js'

const isEven = n => n % 2 === 0

test('when true', () => {
  expect(none(isEven, [ 1, 3, 5, 7 ])).toBeTrue()
})

test('when false curried', () => {
  expect(none(input => input > 1, [ 1, 2, 3 ])).toBeFalse()
})

noop

noop(): void

export function noop(){}

not

not(input: any): boolean

It returns a boolean negated version of input.

R.not(false) // true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.not(false)%20%2F%2F%20true">Try this <strong>R.not</strong> example in Rambda REPL</a>

export function not(input){
  return !input
}

import { not } from './not.js'

test('not', () => {
  expect(not(false)).toBeTrue()
  expect(not(true)).toBeFalse()
  expect(not(0)).toBeTrue()
  expect(not(1)).toBeFalse()
})

nth

nth(index: number, input: string): string

Curried version of input[index].

const list = [1, 2, 3]
const str = 'foo'

const result = [
  R.nth(2, list),
  R.nth(6, list),
  R.nth(0, str),
]
// => [3, undefined, 'f']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20str%20%3D%20'foo'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.nth(2%2C%20list)%2C%0A%20%20R.nth(6%2C%20list)%2C%0A%20%20R.nth(0%2C%20str)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B3%2C%20undefined%2C%20'f'%5D">Try this <strong>R.nth</strong> example in Rambda REPL</a>

export function nth(index, input){
  if (arguments.length === 1) return _input => nth(index, _input)

  const idx = index < 0 ? input.length + index : index

  return Object.prototype.toString.call(input) === '[object String]' ?
    input.charAt(idx) :
    input[ idx ]
}

import { nth } from './nth.js'

test('happy', () => {
  expect(nth(2, [ 1, 2, 3, 4 ])).toBe(3)
})

test('with curry', () => {
  expect(nth(2)([ 1, 2, 3, 4 ])).toBe(3)
})

test('with string and correct index', () => {
  expect(nth(2)('foo')).toBe('o')
})

test('with string and invalid index', () => {
  expect(nth(20)('foo')).toBe('')
})

test('with negative index', () => {
  expect(nth(-3)([ 1, 2, 3, 4 ])).toBe(2)
})

objOf

It creates an object with a single key-value pair.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.objOf('foo'%2C%20'bar')%0A%2F%2F%20%3D%3E%20%7Bfoo%3A%20'bar'%7D">Try this <strong>R.objOf</strong> example in Rambda REPL</a>

of

of<T>(x: T): T[]

R.of(null); // => [null]
R.of([42]); // => [[42]]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.of(null)%3B%20%2F%2F%20%3D%3E%20%5Bnull%5D%0Aconst%20result%20%3D%20R.of(%5B42%5D)%3B%20%2F%2F%20%3D%3E%20%5B%5B42%5D%5D">Try this <strong>R.of</strong> example in Rambda REPL</a>

export function of(value){
  return [ value ]
}

import { of } from './of.js'

test('happy', () => {
  expect(of(3)).toEqual([ 3 ])

  expect(of(null)).toEqual([ null ])
})

ok

ok(...inputs: any[]): (...schemas: any[]) => void | never

It checks if inputs are following schemas specifications according to R.isValid.

If validation fails, it throws.

:boom: It is same as R.pass but instead of returning false, it throws an error.

const result = R.ok(
  1,
  ['foo', 'bar']
)(
  Number,
  [String]
)
// => undefined

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.ok(%0A%20%201%2C%0A%20%20%5B'foo'%2C%20'bar'%5D%0A)(%0A%20%20Number%2C%0A%20%20%5BString%5D%0A)%0A%2F%2F%20%3D%3E%20undefined">Try this <strong>R.ok</strong> example in Rambda REPL</a>

import { any } from './any.js'
import { glue } from './glue.js'
import { fromPrototypeToString, isValid } from './isValid.js'
import { map } from './map.js'
import { type } from './type.js'

export function schemaToString(schema){
  if (type(schema) !== 'Object'){
    return fromPrototypeToString(schema).rule
  }

  return map(x => {
    const { rule, parsed } = fromPrototypeToString(x)
    const xType = type(x)

    if (xType === 'Function' && !parsed) return 'Function'

    return parsed ? rule : xType
  }, schema)
}

export function check(singleInput, schema){
  return isValid({
    input  : { singleInput },
    schema : { singleInput : schema },
  })
}

export function ok(...inputs){
  return (...schemas) => {
    let failedSchema

    const anyError = any((singleInput, i) => {
      const schema = schemas[ i ] === undefined ? schemas[ 0 ] : schemas[ i ]

      const checked = check(singleInput, schema)
      if (!checked){
        failedSchema = JSON.stringify({
          input  : singleInput,
          schema : schemaToString(schema),
        })
      }

      return !checked
    }, inputs)

    if (anyError){
      const errorMessage =
        inputs.length > 1 ?
          glue(`
        Failed R.ok -
        reason: ${ failedSchema }
        all inputs: ${ JSON.stringify(inputs) }
        all schemas: ${ JSON.stringify(schemas.map(schemaToString)) }
      `,
          '\n') :
          `Failed R.ok - ${ failedSchema }`

      throw new Error(errorMessage)
    }
  }
}

import { ok, schemaToString } from './ok.js'

test('happy', () => {
  expect(() => {
    ok(
      1, 'foo', {}
    )(
      'number', 'string', 'object'
    )
  }).not.toThrow()
})

test('when validation fails', () => {
  expect(() => ok(
    1, 'foo', {}
  )(
    'number', 'string', 'string'
  ))
    .toThrowErrorMatchingInlineSnapshot(`
    "Failed R.ok -
    reason: {"input":{},"schema":"string"}
    all inputs: [1,"foo",{}]
    all schemas: ["number","string","string"]"
  `)
})

test('schema in error message', () => {
  const result = schemaToString({
    _a : [ Number ],
    a  : Number,
    b  : x => x > 2,
    c  : [ 'foo', 'bar' ],
    d  : [ { a : String } ],
    e  : 'boolean',
    f  : Array,
    h  : Object,
  })

  expect(result).toMatchInlineSnapshot(`
    {
      "_a": "Array",
      "a": "number",
      "b": "Function",
      "c": "Array",
      "d": "Array",
      "e": "String",
      "f": "array",
      "h": "object",
    }
  `)
})

test('error contains schema', () => {
  try {
    ok(
      1, 'foo', {}
    )(
      { a : Number }, String, String
    )
    expect(false).toBeTrue()
  } catch (e){
    expect(e.message.startsWith('Failed R.ok -')).toBeTruthy()
    expect(e).toBeInstanceOf(Error)
  }
})

test('when not throws with single schema', () => {
  expect(() => ok(
    1, 2, 3
  )('number')).not.toThrow()
})

test('when throws with single schema', () => {
  expect(() => ok(
    1, 2, '3'
  )('number')).toThrowErrorMatchingInlineSnapshot(`
    "Failed R.ok -
    reason: {"input":"3","schema":"number"}
    all inputs: [1,2,"3"]
    all schemas: ["number"]"
  `)
})

test('when throws with single input', () => {
  expect(() => ok('3')('number')).toThrowErrorMatchingInlineSnapshot('"Failed R.ok - {"input":"3","schema":"number"}"')
})

omit

omit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>

It returns a partial copy of an obj without propsToOmit properties.

:boom: When using this method with TypeScript, it is much easier to pass propsToOmit as an array. If passing a string, you will need to explicitly declare the output type.

const obj = {a: 1, b: 2, c: 3}
const propsToOmit = 'a,c,d'
const propsToOmitList = ['a', 'c', 'd']

const result = [
  R.omit(propsToOmit, Record<string, unknown>), 
  R.omit(propsToOmitList, Record<string, unknown>) 
]
// => [{b: 2}, {b: 2}]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0Aconst%20propsToOmit%20%3D%20'a%2Cc%2Cd'%0Aconst%20propsToOmitList%20%3D%20%5B'a'%2C%20'c'%2C%20'd'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.omit(propsToOmit%2C%20Record%3Cstring%2C%20unknown%3E)%2C%20%0A%20%20R.omit(propsToOmitList%2C%20Record%3Cstring%2C%20unknown%3E)%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B%7Bb%3A%202%7D%2C%20%7Bb%3A%202%7D%5D">Try this <strong>R.omit</strong> example in Rambda REPL</a>

import { createPath } from './_internals/createPath.js'
import { includes } from './_internals/includes.js'

export function omit(propsToOmit, obj){
  if (arguments.length === 1) return _obj => omit(propsToOmit, _obj)

  if (obj === null || obj === undefined)
    return undefined

  const propsToOmitValue = createPath(propsToOmit, ',')
  const willReturn = {}

  for (const key in obj)
    if (!includes(key, propsToOmitValue))
      willReturn[ key ] = obj[ key ]

  return willReturn
}

import { omit } from './omit.js'

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = omit('a,c', obj)
  const resultCurry = omit('a,c')(obj)
  const expectedResult = { b : 2 }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test.only('with number as property to omit', () => {
  const obj = {
    1 : 1,
    b : 2,
  }
  const result = omit([ 1 ], obj)
  expect(result).toEqual({ b : 2 })
})

test('with null', () => {
  expect(omit('a,b', null)).toBeUndefined()
})

test('happy', () => {
  expect(omit([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ b : 'bar' })
})

on

It passes the two inputs through unaryFn and then the results are passed as inputs the the binaryFn to receive the final result(binaryFn(unaryFn(FIRST_INPUT), unaryFn(SECOND_INPUT))).

This method is also known as P combinator.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.on((a%2C%20b)%20%3D%3E%20a%20%2B%20b%2C%20R.prop('a')%2C%20%7Bb%3A0%2C%20a%3A1%7D%2C%20%7Ba%3A2%7D)%0A%2F%2F%20%3D%3E%203">Try this <strong>R.on</strong> example in Rambda REPL</a>

once

once<T extends AnyFunction, C = unknown>(fn: T, context?: C): T

It returns a function, which invokes only once fn function.

let result = 0
const addOnce = R.once((x) => result = result + x)

addOnce(1)
addOnce(1)
// => 1

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?let%20result%20%3D%200%0Aconst%20addOnce%20%3D%20R.once((x)%20%3D%3E%20result%20%3D%20result%20%2B%20x)%0A%0AaddOnce(1)%0Aconst%20result%20%3D%20addOnce(1)%0A%2F%2F%20%3D%3E%201">Try this <strong>R.once</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

function onceFn(fn, context){
  let result

  return function (){
    if (fn){
      result = fn.apply(context || this, arguments)
      fn = null
    }

    return result
  }
}

export function once(fn, context){
  if (arguments.length === 1){
    const wrap = onceFn(fn, context)

    return curry(wrap)
  }

  return onceFn(fn, context)
}

import { once } from './once.js'

test('with counter', () => {
  let counter = 0
  const runOnce = once(x => {
    counter++

    return x + 2
  })
  expect(runOnce(1)).toBe(3)
  runOnce(1)
  runOnce(1)
  runOnce(1)
  expect(counter).toBe(1)
})

test('happy path', () => {
  const addOneOnce = once((
    a, b, c
  ) => a + b + c, 1)

  expect(addOneOnce(
    10, 20, 30
  )).toBe(60)
  expect(addOneOnce(40)).toBe(60)
})

test('with context', () => {
  const context = { name: 'fris' }
  const getNameOnce = once(function (){
    return this.name
  }, context)

  expect(getNameOnce()).toBe('fris')
  expect(getNameOnce()).toBe('fris')
  expect(getNameOnce()).toBe('fris')
})

or

Logical OR

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.or(false%2C%20true)%3B%20%2F%2F%20%3D%3E%20true%0AR.or(false%2C%20false)%3B%20%2F%2F%20%3D%3E%20false%0Aconst%20result%20%3D%20R.or(false%2C%20'foo')%3B%20%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.or</strong> example in Rambda REPL</a>

over

over<S, A>(lens: Lens<S, A>): {
  (fn: (a: A) => A): (value: S) => S

It returns a copied Object or Array with modified value received by applying function fn to lens focus.

const headLens = R.lensIndex(0)
 
R.over(headLens, R.toUpper, ['foo', 'bar', 'baz']) // => ['FOO', 'bar', 'baz']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20headLens%20%3D%20R.lensIndex(0)%0A%20%0Aconst%20result%20%3D%20R.over(headLens%2C%20R.toUpper%2C%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D)%20%2F%2F%20%3D%3E%20%5B'FOO'%2C%20'bar'%2C%20'baz'%5D">Try this <strong>R.over</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

const Identity = x => ({
  x,
  map : fn => Identity(fn(x)),
})

function overFn(
  lens, fn, object
){
  return lens(x => Identity(fn(x)))(object).x
}

export const over = curry(overFn)

import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { lensIndex } from './lensIndex.js'
import { lensPath } from './lensPath.js'
import { over } from './over.js'
import { prop } from './prop.js'
import { toUpper } from './toUpper.js'

const testObject = {
  foo : 'bar',
  baz : {
    a : 'x',
    b : 'y',
  },
}

test('assoc lens', () => {
  const assocLens = lens(prop('foo'), assoc('foo'))
  const result = over(
    assocLens, toUpper, testObject
  )
  const expected = {
    ...testObject,
    foo : 'BAR',
  }
  expect(result).toEqual(expected)
})

test('path lens', () => {
  const pathLens = lensPath('baz.a')
  const result = over(
    pathLens, toUpper, testObject
  )
  const expected = {
    ...testObject,
    baz : {
      a : 'X',
      b : 'y',
    },
  }
  expect(result).toEqual(expected)
})

test('index lens', () => {
  const indexLens = lensIndex(0)
  const result = over(indexLens, toUpper)([ 'foo', 'bar' ])
  expect(result).toEqual([ 'FOO', 'bar' ])
})

partial

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T

It is very similar to R.curry, but you can pass initial arguments when you create the curried function.

R.partial will keep returning a function until all the arguments that the function fn expects are passed. The name comes from the fact that you partially inject the inputs.

:boom: Rambda's partial doesn't need the input arguments to be wrapped as array.

const fn = (title, firstName, lastName) => {
  return title + ' ' + firstName + ' ' + lastName + '!'
}

const canPassAnyNumberOfArguments = R.partial(fn, 'Hello')
const ramdaStyle = R.partial(fn, ['Hello'])

const finalFn = canPassAnyNumberOfArguments('Foo')

finalFn('Bar') // =>  'Hello, Foo Bar!'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(title%2C%20firstName%2C%20lastName)%20%3D%3E%20%7B%0A%20%20return%20title%20%2B%20'%20'%20%2B%20firstName%20%2B%20'%20'%20%2B%20lastName%20%2B%20'!'%0A%7D%0A%0Aconst%20canPassAnyNumberOfArguments%20%3D%20R.partial(fn%2C%20'Hello')%0Aconst%20ramdaStyle%20%3D%20R.partial(fn%2C%20%5B'Hello'%5D)%0A%0Aconst%20finalFn%20%3D%20canPassAnyNumberOfArguments('Foo')%0A%0Aconst%20result%20%3D%20finalFn('Bar')%20%2F%2F%20%3D%3E%20%20'Hello%2C%20Foo%20Bar!'">Try this <strong>R.partial</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

export function partial(fn, ...args){
  const len = fn.length

  // If a single array argument is given, those are the args (a la Ramda).
  // Otherwise, the variadic arguments are the args.
  const argList = args.length === 1 && isArray(args[0]) ? args[0] : args

  return (...rest) => {
    if (argList.length + rest.length >= len){
      return fn(...argList, ...rest)
    }

    return partial(fn, ...[ ...argList, ...rest ])
  }
}

import { partial } from './partial.js'
import { type } from './type.js'

const greet = (
  salutation, title, firstName, lastName
) =>
  [salutation, title, firstName, lastName]

test('happy', () => {
  const canPassAnyNumberOfArguments = partial(
    greet, 'Hello', 'Ms.'
  )
  const fn = canPassAnyNumberOfArguments('foo')
  const sayHello = partial(greet, [ 'Hello' ])
  const sayHelloRamda = partial(sayHello, [ 'Ms.' ])

  expect(type(fn)).toBe('Function')

  expect(fn('bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
  expect(sayHelloRamda('foo', 'bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
})

test('extra arguments are ignored', () => {
  const canPassAnyNumberOfArguments = partial(
    greet, 'Hello', 'Ms.'
  )
  const fn = canPassAnyNumberOfArguments('foo')

  expect(type(fn)).toBe('Function')

  expect(fn(
    'bar', 1, 2
  )).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
})

test('when array is input', () => {
  const fooFn = (
    a, b, c, d
  ) => ({
    a,
    b,
    c,
    d,
  })
  const barFn = partial(
    fooFn, [ 1, 2 ], []
  )

  expect(barFn(1, 2)).toEqual({
    a : [ 1, 2 ],
    b : [],
    c : 1,
    d : 2,
  })
})

test('ramda spec', () => {
  const sayHello = partial(greet, 'Hello')
  const sayHelloToMs = partial(sayHello, 'Ms.')

  expect(sayHelloToMs('Jane', 'Jones')).toStrictEqual(['Hello', 'Ms.', 'Jane', 'Jones'])
})

partialCurry

partialCurry<Input, PartialInput, Output>(
  fn: (input: Input) => Output, 
  partialInput: PartialInput,
): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output

Same as R.partialObject.

When Ramda introduced R.partialObject, Rambdax already had such method, i.e. R.partialCurry. So this method is kept for backward compatibility.

:boom: Function input can be asynchronous

export { partialObject as partialCurry } from './partialObject.js'

partialObject

partialObject<Input, PartialInput, Output>(
  fn: (input: Input) => Output, 
  partialInput: PartialInput,
): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output

R.partialObject is a curry helper designed specifically for functions accepting object as a single argument.

Initially the function knows only a part from the whole input object and then R.partialObject helps in preparing the function for the second part, when it receives the rest of the input.

:boom: Function input can be asynchronous

const fn = ({ a, b, c }) => a + b + c
const curried = R.partialObject(fn, { a : 1 })
const result = curried({
  b : 2,
  c : 3,
})
// => 6

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(%7B%20a%2C%20b%2C%20c%20%7D)%20%3D%3E%20a%20%2B%20b%20%2B%20c%0Aconst%20curried%20%3D%20R.partialObject(fn%2C%20%7B%20a%20%3A%201%20%7D)%0Aconst%20result%20%3D%20curried(%7B%0A%20%20b%20%3A%202%2C%0A%20%20c%20%3A%203%2C%0A%7D)%0A%2F%2F%20%3D%3E%206">Try this <strong>R.partialObject</strong> example in Rambda REPL</a>

import { mergeDeepRight } from './mergeDeepRight.js'

export function partialObject(fn, input){
  return nextInput => fn(mergeDeepRight(nextInput, input))
}

import { delay } from './delay.js'
import { partialObject } from './partialObject.js'
import { type } from './type.js'

test('with plain function', () => {
  const fn = ({ a, b, c }) => a + b + c
  const curried = partialObject(fn, { a : 1 })

  expect(type(curried)).toBe('Function')
  expect(curried({
    b : 2,
    c : 3,
  })).toBe(6)
})

test('with function that throws an error', () => {
  const fn = ({ a, b, c }) => {
    throw new Error('foo')
  }
  const curried = partialObject(fn, { a : 1 })

  expect(type(curried)).toBe('Function')
  expect(() =>
    curried({
      b : 2,
      c : 3,
    })).toThrowErrorMatchingInlineSnapshot('"foo"')
})

test('with async', async () => {
  const fn = async ({ a, b, c }) => {
    await delay(100)

    return a + b + c
  }

  const curried = partialObject(fn, { a : 1 })

  const result = await curried({
    b : 2,
    c : 3,
  })

  expect(result).toBe(6)
})

test('async function throwing an error', async () => {
  const fn = async ({ a, b, c }) => {
    await delay(100)
    throw new Error('foo')
  }

  const curried = partialObject(fn, { a : 1 })

  try {
    await curried({
      b : 2,
      c : 3,
    })
    expect(true).toBeFalsy()
  } catch (e){
    expect(e.message).toBe('foo')
  }
})

partition

partition<T>(
  predicate: Predicate<T>,
  input: T[]
): [T[], T[]]

It will return array of two objects/arrays according to predicate function. The first member holds all instances of input that pass the predicate function, while the second member - those who doesn't.

const list = [1, 2, 3]
const obj = {a: 1, b: 2, c: 3}
const predicate = x => x > 2

const result = [
  R.partition(predicate, list),
  R.partition(predicate, Record<string, unknown>)
]
const expected = [
  [[3], [1, 2]],
  [{c: 3},  {a: 1, b: 2}],
]
// `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%202%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.partition(predicate%2C%20list)%2C%0A%20%20R.partition(predicate%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0Aconst%20expected%20%3D%20%5B%0A%20%20%5B%5B3%5D%2C%20%5B1%2C%202%5D%5D%2C%0A%20%20%5B%7Bc%3A%203%7D%2C%20%20%7Ba%3A%201%2C%20b%3A%202%7D%5D%2C%0A%5D%0A%2F%2F%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.partition</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

export function partitionObject(predicate, iterable){
  const yes = {}
  const no = {}
  Object.entries(iterable).forEach(([ prop, value ]) => {
    if (predicate(value, prop)){
      yes[ prop ] = value
    } else {
      no[ prop ] = value
    }
  })

  return [ yes, no ]
}

export function partitionArray(
  predicate, list, indexed = false
){
  const yes = []
  const no = []
  let counter = -1

  while (counter++ < list.length - 1){
    if (
      indexed ? predicate(list[ counter ], counter) : predicate(list[ counter ])
    ){
      yes.push(list[ counter ])
    } else {
      no.push(list[ counter ])
    }
  }

  return [ yes, no ]
}

export function partition(predicate, iterable){
  if (arguments.length === 1){
    return listHolder => partition(predicate, listHolder)
  }
  if (!isArray(iterable)) return partitionObject(predicate, iterable)

  return partitionArray(predicate, iterable)
}

import { partition } from './partition.js'

test('with array', () => {
  const predicate = x => x > 2
  const list = [ 1, 2, 3, 4 ]

  const result = partition(predicate, list)
  const expectedResult = [
    [ 3, 4 ],
    [ 1, 2 ],
  ]

  expect(result).toEqual(expectedResult)
})

test('with object', () => {
  const predicate = (value, prop) => {
    expect(typeof prop).toBe('string')

    return value > 2
  }
  const hash = {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  }

  const result = partition(predicate)(hash)
  const expectedResult = [
    {
      c : 3,
      d : 4,
    },
    {
      a : 1,
      b : 2,
    },
  ]

  expect(result).toEqual(expectedResult)
})

test('readme example', () => {
  const list = [ 1, 2, 3 ]
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const predicate = x => x > 2

  const result = [ partition(predicate, list), partition(predicate, obj) ]
  const expected = [
    [ [ 3 ], [ 1, 2 ] ],
    [
      { c : 3 },
      {
        a : 1,
        b : 2,
      },
    ],
  ]
  expect(result).toEqual(expected)
})

partitionIndexed

pass

pass(...inputs: any[]): (...rules: any[]) => boolean

It checks if inputs are following schemas specifications according to R.isValid.

const result = R.pass(
  1,
  ['foo','bar']
)(
  Number,
  [String]
)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.pass(%0A%20%201%2C%0A%20%20%5B'foo'%2C'bar'%5D%0A)(%0A%20%20Number%2C%0A%20%20%5BString%5D%0A)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.pass</strong> example in Rambda REPL</a>

import { any } from './any.js'
import { check } from './ok.js'

export function pass(...inputs){
  return (...schemas) =>
    any((x, i) => {
      const schema = schemas[ i ] === undefined ? schemas[ 0 ] : schemas[ i ]

      return !check(x, schema)
    }, inputs) === false
}

import { pass } from './pass.js'

test('true on success', () => {
  const result = pass(
    1, 'foo', {}
  )(
    'number', 'string', 'object'
  )

  expect(result).toBeTrue()
})

test('false on failure', () => {
  expect(pass(
    1, 'foo', {}
  )(
    'number', 'string', 'string'
  )).toBeFalse()
})

test('true when single schema', () => {
  expect(pass(
    1, 2, 3
  )('number')).toBeTrue()
})

test('false when single schema', () => {
  expect(pass(
    1, 'foo', {}
  )('number')).toBeFalse()
})

test('array of schemas', () => {
  const result = pass([ { a : 1 }, { a : 2 }, { a : 3 } ])([ { a : Number } ])
  expect(result).toBeTruthy()
})

test('reame example', () => {
  const result = pass(1, [ 'foo', 'bar' ])(Number, [ String ])
  expect(result).toBeTruthy()
})

path

path<S, K0 extends keyof S = keyof S>(path: [K0], obj: S): S[K0]

If pathToSearch is 'a.b' then it will return 1 if obj is {a:{b:1}}.

It will return undefined, if such path is not found.

:boom: String annotation of pathToSearch is one of the differences between Rambda and Ramda.

const obj = {a: {b: 1}}
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const result = [
  R.path(pathToSearch, obj),
  R.path(pathToSearchList, obj),
  R.path('a.b.c.d', obj)
]
// => [1, 1, undefined]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%20%7Bb%3A%201%7D%7D%0Aconst%20pathToSearch%20%3D%20'a.b'%0Aconst%20pathToSearchList%20%3D%20%5B'a'%2C%20'b'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.path(pathToSearch%2C%20obj)%2C%0A%20%20R.path(pathToSearchList%2C%20obj)%2C%0A%20%20R.path('a.b.c.d'%2C%20obj)%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%201%2C%20undefined%5D">Try this <strong>R.path</strong> example in Rambda REPL</a>

import { createPath } from './_internals/createPath.js'

export function pathFn(pathInput, obj){
  let willReturn = obj
  let counter = 0

  const pathArrValue = createPath(pathInput)

  while (counter < pathArrValue.length){
    if (willReturn === null || willReturn === undefined){
      return undefined
    }
    if (willReturn[ pathArrValue[ counter ] ] === null) return undefined

    willReturn = willReturn[ pathArrValue[ counter ] ]
    counter++
  }

  return willReturn
}

export function path(pathInput, obj){
  if (arguments.length === 1) return _obj => path(pathInput, _obj)

  if (obj === null || obj === undefined){
    return undefined
  }

  return pathFn(pathInput, obj)
}

import { path } from './path.js'

test('with array inside object', () => {
  const obj = { a : { b : [ 1, { c : 1 } ] } }

  expect(path('a.b.1.c', obj)).toBe(1)
})

test('works with undefined', () => {
  const obj = { a : { b : { c : 1 } } }

  expect(path('a.b.c.d.f', obj)).toBeUndefined()
  expect(path('foo.babaz', undefined)).toBeUndefined()
  expect(path('foo.babaz')(undefined)).toBeUndefined()
})

test('works with string instead of array', () => {
  expect(path('foo.bar.baz')({ foo : { bar : { baz : 'yes' } } })).toBe('yes')
})

test('path', () => {
  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : { baz : 'yes' } } })).toBe('yes')
  expect(path([ 'foo', 'bar', 'baz' ])(null)).toBeUndefined()
  expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : 'baz' } })).toBeUndefined()
})

test('with number string in between', () => {
	expect(path(['a','1','b'], {a: [{b: 1}, {b: 2}]})).toBe(2)
})

test('null is not a valid path', () => {
  expect(path('audio_tracks', {
    a            : 1,
    audio_tracks : null,
  })).toBeUndefined()
})

pathEq

pathEq(pathToSearch: Path, target: any, input: any): boolean

It returns true if pathToSearch of input object is equal to target value.

pathToSearch is passed to R.path, which means that it can be either a string or an array. Also equality between target and the found value is determined by R.equals.

const path = 'a.b'
const target = {c: 1}
const input = {a: {b: {c: 1}}}

const result = R.pathEq(
  path,
  target,
  input
)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20path%20%3D%20'a.b'%0Aconst%20target%20%3D%20%7Bc%3A%201%7D%0Aconst%20input%20%3D%20%7Ba%3A%20%7Bb%3A%20%7Bc%3A%201%7D%7D%7D%0A%0Aconst%20result%20%3D%20R.pathEq(%0A%20%20path%2C%0A%20%20target%2C%0A%20%20input%0A)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.pathEq</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { equals } from './equals.js'
import { path } from './path.js'

function pathEqFn(
  pathToSearch, target, input
){
  return equals(path(pathToSearch, input), target)
}

export const pathEq = curry(pathEqFn)

import { pathEq } from './pathEq.js'

test('when true', () => {
  const path = 'a.b'
  const obj = { a : { b : { c : 1 } } }
  const target = { c : 1 }

  expect(pathEq(
    path, target, obj
  )).toBeTrue()
})

test('when false', () => {
  const path = 'a.b'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(path, target)(obj)).toBeFalse()
})

test('when wrong path', () => {
  const path = 'foo.bar'
  const obj = { a : { b : 1 } }
  const target = 2

  expect(pathEq(
    path, target, obj
  )).toBeFalse()
})

pathOr

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T

It reads obj input and returns either R.path(pathToSearch, Record<string, unknown>) result or defaultValue input.

const defaultValue = 'DEFAULT_VALUE'
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const obj = {
  a : {
    b : 1
  }
}

const result = [
  R.pathOr(DEFAULT_VALUE, pathToSearch, Record<string, unknown>),
  R.pathOr(DEFAULT_VALUE, pathToSearchList, Record<string, unknown>), 
  R.pathOr(DEFAULT_VALUE, 'a.b.c', Record<string, unknown>)
]
// => [1, 1, 'DEFAULT_VALUE']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20defaultValue%20%3D%20'DEFAULT_VALUE'%0Aconst%20pathToSearch%20%3D%20'a.b'%0Aconst%20pathToSearchList%20%3D%20%5B'a'%2C%20'b'%5D%0A%0Aconst%20obj%20%3D%20%7B%0A%20%20a%20%3A%20%7B%0A%20%20%20%20b%20%3A%201%0A%20%20%7D%0A%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.pathOr(DEFAULT_VALUE%2C%20pathToSearch%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pathOr(DEFAULT_VALUE%2C%20pathToSearchList%2C%20Record%3Cstring%2C%20unknown%3E)%2C%20%0A%20%20R.pathOr(DEFAULT_VALUE%2C%20'a.b.c'%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%201%2C%20'DEFAULT_VALUE'%5D">Try this <strong>R.pathOr</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { defaultTo } from './defaultTo.js'
import { path } from './path.js'

function pathOrFn(
  defaultValue, pathInput, obj
){
  return defaultTo(defaultValue, path(pathInput, obj))
}

export const pathOr = curry(pathOrFn)

import { pathOr } from './pathOr.js'

test('with undefined', () => {
  const result = pathOr(
    'foo', 'x.y', { x : { y : 1 } }
  )

  expect(result).toBe(1)
})

test('with null', () => {
  const result = pathOr(
    'foo', 'x.y', null
  )

  expect(result).toBe('foo')
})

test('with NaN', () => {
  const result = pathOr(
    'foo', 'x.y', NaN
  )

  expect(result).toBe('foo')
})

test('curry case (x)(y)(z)', () => {
  const result = pathOr('foo')('x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toBe('foo')
})

test('curry case (x)(y,z)', () => {
  const result = pathOr('foo', 'x.y.z')({ x : { y : { a : 1 } } })

  expect(result).toBe('foo')
})

test('curry case (x,y)(z)', () => {
  const result = pathOr('foo')('x.y.z', { x : { y : { a : 1 } } })

  expect(result).toBe('foo')
})

paths

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[]

It loops over members of pathsToSearch as singlePath and returns the array produced by R.path(singlePath, Record<string, unknown>).

Because it calls R.path, then singlePath can be either string or a list.

const obj = {
  a : {
    b : {
      c : 1,
      d : 2
    }
  }
}

const result = R.paths([
  'a.b.c',
  'a.b.d',
  'a.b.c.d.e',
], Record<string, unknown>)
// => [1, 2, undefined]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%20%3A%20%7B%0A%20%20%20%20b%20%3A%20%7B%0A%20%20%20%20%20%20c%20%3A%201%2C%0A%20%20%20%20%20%20d%20%3A%202%0A%20%20%20%20%7D%0A%20%20%7D%0A%7D%0A%0Aconst%20result%20%3D%20R.paths(%5B%0A%20%20'a.b.c'%2C%0A%20%20'a.b.d'%2C%0A%20%20'a.b.c.d.e'%2C%0A%5D%2C%20Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%20undefined%5D">Try this <strong>R.paths</strong> example in Rambda REPL</a>

import { path } from './path.js'

export function paths(pathsToSearch, obj){
  if (arguments.length === 1){
    return _obj => paths(pathsToSearch, _obj)
  }

  return pathsToSearch.map(singlePath => path(singlePath, obj))
}

import { paths } from './paths.js'

const obj = {
  a : {
    b : {
      c : 1,
      d : 2,
    },
  },
  p : [ { q : 3 } ],
  x : {
    y : 'FOO',
    z : [ [ {} ] ],
  },
}

test('with string path + curry', () => {
  const pathsInput = [ 'a.b.d', 'p.q' ]
  const expected = [ 2, undefined ]
  const result = paths(pathsInput, obj)
  const curriedResult = paths(pathsInput)(obj)

  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
})

test('with array path', () => {
  const result = paths([
    [ 'a', 'b', 'c' ],
    [ 'x', 'y' ],
  ],
  obj)

  expect(result).toEqual([ 1, 'FOO' ])
})

test('takes a paths that contains indices into arrays', () => {
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 0, 0 ],
  ],
  obj)).toEqual([ 3, {} ])
  expect(paths([
    [ 'p', 0, 'q' ],
    [ 'x', 'z', 2, 1 ],
  ],
  obj)).toEqual([ 3, undefined ])
})

test('gets a deep property\'s value from objects', () => {
  expect(paths([ [ 'a', 'b' ] ], obj)).toEqual([ obj.a.b ])
  expect(paths([ [ 'p', 0 ] ], obj)).toEqual([ obj.p[ 0 ] ])
})

test('returns undefined for items not found', () => {
  expect(paths([ [ 'a', 'x', 'y' ] ], obj)).toEqual([ undefined ])
  expect(paths([ [ 'p', 2 ] ], obj)).toEqual([ undefined ])
})

pathSatisfies

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.pathSatisfies(%0A%20%20x%20%3D%3E%20x%20%3E%200%2C%0A%20%20%5B'a'%2C%20'b'%2C%20'c'%5D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%20%7Bc%3A%201%7D%7D%7D%0A)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.pathSatisfies</strong> example in Rambda REPL</a>

pick

pick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>

It returns a partial copy of an input containing only propsToPick properties.

input can be either an object or an array.

String annotation of propsToPick is one of the differences between Rambda and Ramda.

:boom: When using this method with TypeScript, it is much easier to pass propsToPick as an array. If passing a string, you will need to explicitly declare the output type.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const list = [1, 2, 3, 4]
const propsToPick = 'a,foo'
const propsToPickList = ['a', 'foo']

const result = [
  R.pick(propsToPick, Record<string, unknown>),
  R.pick(propsToPickList, Record<string, unknown>),
  R.pick('a,bar', Record<string, unknown>),
  R.pick('bar', Record<string, unknown>),
  R.pick([0, 3, 5], list),
  R.pick('0,3,5', list),
]

const expected = [
  {a:1, foo: 'cherry'},
  {a:1, foo: 'cherry'},
  {a:1},
  {},
  {0: 1, 3: 4},
  {0: 1, 3: 4},
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%20false%2C%0A%20%20foo%3A%20'cherry'%0A%7D%0Aconst%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20propsToPick%20%3D%20'a%2Cfoo'%0Aconst%20propsToPickList%20%3D%20%5B'a'%2C%20'foo'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.pick(propsToPick%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick(propsToPickList%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick('a%2Cbar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick('bar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick(%5B0%2C%203%2C%205%5D%2C%20list)%2C%0A%20%20R.pick('0%2C3%2C5'%2C%20list)%2C%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%7D%2C%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%7D%2C%0A%20%20%7Ba%3A1%7D%2C%0A%20%20%7B%7D%2C%0A%20%20%7B0%3A%201%2C%203%3A%204%7D%2C%0A%20%20%7B0%3A%201%2C%203%3A%204%7D%2C%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.pick</strong> example in Rambda REPL</a>

import { createPath } from './_internals/createPath.js'

export function pick(propsToPick, input){
  if (arguments.length === 1) return _input => pick(propsToPick, _input)

  if (input === null || input === undefined){
    return undefined
  }
  const keys = createPath(propsToPick, ',')
  const willReturn = {}
  let counter = 0

  while (counter < keys.length){
    if (keys[ counter ] in input){
      willReturn[ keys[ counter ] ] = input[ keys[ counter ] ]
    }
    counter++
  }

  return willReturn
}

import { pick } from './pick.js'

const obj = {
  a : 1,
  b : 2,
  c : 3,
}

test('props to pick is a string', () => {
  const result = pick('a,c', obj)
  const resultCurry = pick('a,c')(obj)
  const expectedResult = {
    a : 1,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('when prop is missing', () => {
  const result = pick('a,d,f', obj)
  expect(result).toEqual({ a : 1 })
})

test('with list indexes as props', () => {
  const list = [ 1, 2, 3 ]
  const expected = {
    0 : 1,
    2 : 3,
  }
  expect(pick([ 0, 2, 3 ], list)).toEqual(expected)
  expect(pick('0,2,3', list)).toEqual(expected)
})

test('props to pick is an array', () => {
  expect(pick([ 'a', 'c' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    c : 'baz',
  })

  expect(pick([ 'a', 'd', 'e', 'f' ])({
    a : 'foo',
    b : 'bar',
    c : 'baz',
  })).toEqual({ a : 'foo' })

  expect(pick('a,d,e,f')(null)).toBeUndefined()
})

test('works with list as input and number as props - props to pick is an array', () => {
  const result = pick([ 1, 2 ], [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('works with list as input and number as props - props to pick is a string', () => {
  const result = pick('1,2', [ 'a', 'b', 'c', 'd' ])
  expect(result).toEqual({
    1 : 'b',
    2 : 'c',
  })
})

test('with symbol', () => {
  const symbolProp = Symbol('s')
  expect(pick([ symbolProp ], { [ symbolProp ] : 'a' })).toMatchInlineSnapshot(`
{
  Symbol(s): "a",
}
`)
})

pickAll

pickAll<T, K extends keyof T>(propsToPicks: K[], input: T): Pick<T, K>

Same as R.pick but it won't skip the missing props, i.e. it will assign them to undefined.

:boom: When using this method with TypeScript, it is much easier to pass propsToPick as an array. If passing a string, you will need to explicitly declare the output type.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const propsToPick = 'a,foo,bar'
const propsToPickList = ['a', 'foo', 'bar']

const result = [
  R.pickAll(propsToPick, Record<string, unknown>),
  R.pickAll(propsToPickList, Record<string, unknown>),
  R.pickAll('a,bar', Record<string, unknown>),
  R.pickAll('bar', Record<string, unknown>),
]
const expected = [
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, bar: undefined},
  {bar: undefined}
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%20false%2C%0A%20%20foo%3A%20'cherry'%0A%7D%0Aconst%20propsToPick%20%3D%20'a%2Cfoo%2Cbar'%0Aconst%20propsToPickList%20%3D%20%5B'a'%2C%20'foo'%2C%20'bar'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.pickAll(propsToPick%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pickAll(propsToPickList%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pickAll('a%2Cbar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pickAll('bar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%5D%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%2C%20bar%3A%20undefined%7D%2C%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%2C%20bar%3A%20undefined%7D%2C%0A%20%20%7Ba%3A1%2C%20bar%3A%20undefined%7D%2C%0A%20%20%7Bbar%3A%20undefined%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.pickAll</strong> example in Rambda REPL</a>

import { createPath } from './_internals/createPath.js'

export function pickAll(propsToPick, obj){
  if (arguments.length === 1) return _obj => pickAll(propsToPick, _obj)

  if (obj === null || obj === undefined){
    return undefined
  }
  const keysValue = createPath(propsToPick, ',')
  const willReturn = {}
  let counter = 0

  while (counter < keysValue.length){
    if (keysValue[ counter ] in obj){
      willReturn[ keysValue[ counter ] ] = obj[ keysValue[ counter ] ]
    } else {
      willReturn[ keysValue[ counter ] ] = undefined
    }
    counter++
  }

  return willReturn
}

import { pickAll } from './pickAll.js'

test('when input is undefined or null', () => {
  expect(pickAll('a', null)).toBeUndefined()
  expect(pickAll('a', undefined)).toBeUndefined()
})

test('with string as condition', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
  }
  const result = pickAll('a,c', obj)
  const resultCurry = pickAll('a,c')(obj)
  const expectedResult = {
    a : 1,
    b : undefined,
    c : 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with array as condition', () => {
  expect(pickAll([ 'a', 'b', 'c' ], {
    a : 'foo',
    c : 'baz',
  })).toEqual({
    a : 'foo',
    b : undefined,
    c : 'baz',
  })
})

pickBy

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.pickBy(%0A%20%20x%20%3D%3E%20x%20%3E%201%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0A)%0A%2F%2F%20%3D%3E%20%7Bb%3A%202%2C%20c%3A%203%7D">Try this <strong>R.pickBy</strong> example in Rambda REPL</a>

pipe

It performs left-to-right function composition.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.pipe(%0A%20%20R.filter(val%20%3D%3E%20val%20%3E%202)%2C%0A%20%20R.map(a%20%3D%3E%20a%20*%202)%0A)(%5B1%2C%202%2C%203%2C%204%5D)%0A%0A%2F%2F%20%3D%3E%20%5B6%2C%208%5D">Try this <strong>R.pipe</strong> example in Rambda REPL</a>

pipeAsync

Asynchronous version of R.pipe, but it accepts only one argument as input(instead of multiple as regular pipe). It awaits the result of each function before passing it to the next. Returns a Promise of the result.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20add%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20%2B%201%0A%7D%0Aconst%20multiply%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20return%20x%20*%202%20%0A%7D%0A%0Aconst%20result%20%3D%20await%20R.pipeAsync(%0A%20%20add%2C%0A%20%20multiply%0A)(1)%0A%2F%2F%20%60result%60%20resolves%20to%20%604%60">Try this <strong>R.pipeAsync</strong> example in Rambda REPL</a>

piped

piped<A, B>(input: A, fn0: (x: A) => B) : B

It is basically R.pipe, but instead of passing input argument as R.pipe(...)(input), you pass it as the first argument.

const result = R.piped(
  [1, 2, 3],
  R.filter(x => x > 1),
  R.map(x => x*10),
)
// => [20, 30]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.piped(%0A%20%20%5B1%2C%202%2C%203%5D%2C%0A%20%20R.filter(x%20%3D%3E%20x%20%3E%201)%2C%0A%20%20R.map(x%20%3D%3E%20x*10)%2C%0A)%0A%2F%2F%20%3D%3E%20%5B20%2C%2030%5D">Try this <strong>R.piped</strong> example in Rambda REPL</a>

import { pipe } from './pipe.js'

export function piped(...inputs){
  const [ input, ...fnList ] = inputs

  return pipe(...fnList)(input)
}

import { add } from './add.js'
import { filter } from './filter.js'
import { map } from './map.js'
import { piped } from './piped.js'

test('happy', () => {
  const result = piped(
    [ 1, 2, 3 ],
    filter(x => x > 1),
    map(x => x * 10),
    map(add(1))
  )
  const expectedResult = [ 21, 31 ]

  expect(result).toEqual(expectedResult)
})

pipedAsync

It accepts input as first argument and series of functions as next arguments. It is same as R.piped but with support for asynchronous functions like R.pipeAsync.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20await%20R.pipedAsync(%0A%20%20100%2C%0A%20%20async%20x%20%3D%3E%20%7B%0A%20%20%20%20await%20R.delay(100)%0A%20%20%20%20return%20x%20%2B%202%0A%20%20%7D%2C%0A%20%20R.add(2)%2C%0A%20%20async%20x%20%3D%3E%20%7B%0A%20%20%20%20const%20delayed%20%3D%20await%20R.delay(100)%0A%20%20%20%20return%20delayed%20%2B%20x%0A%20%20%7D%0A)%0A%2F%2F%20%60result%60%20resolves%20to%20%60RAMBDAX_DELAY104%60">Try this <strong>R.pipedAsync</strong> example in Rambda REPL</a>

pluck

pluck<K extends keyof T, T>(property: K, list: T[]): T[K][]

It returns list of the values of property taken from the all objects inside list.

const list = [{a: 1}, {a: 2}, {b: 3}]
const property = 'a'

const result = R.pluck(property, list) 
// => [1, 2]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A%201%7D%2C%20%7Ba%3A%202%7D%2C%20%7Bb%3A%203%7D%5D%0Aconst%20property%20%3D%20'a'%0A%0Aconst%20result%20%3D%20R.pluck(property%2C%20list)%20%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.pluck</strong> example in Rambda REPL</a>

import { map } from './map.js'

export function pluck(property, list){
  if (arguments.length === 1) return _list => pluck(property, _list)

  const willReturn = []

  map(x => {
    if (x[ property ] !== undefined){
      willReturn.push(x[ property ])
    }
  }, list)

  return willReturn
}

import { pluck } from './pluck.js'

test('happy', () => {
  expect(pluck('a')([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ 1, 2 ])
})

test('with undefined', () => {
  expect(pluck(undefined)([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ ])
})

test('with number', () => {
  const input = [
    [ 1, 2 ],
    [ 3, 4 ],
  ]

  expect(pluck(0, input)).toEqual([ 1, 3 ])
})

prepend

prepend<T>(xToPrepend: T, iterable: T[]): T[]

It adds element x at the beginning of list.

const result = R.prepend('foo', ['bar', 'baz'])
// => ['foo', 'bar', 'baz']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.prepend('foo'%2C%20%5B'bar'%2C%20'baz'%5D)%0A%2F%2F%20%3D%3E%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D">Try this <strong>R.prepend</strong> example in Rambda REPL</a>

export function prepend(x, input){
  if (arguments.length === 1) return _input => prepend(x, _input)

  if (typeof input === 'string') return [ x ].concat(input.split(''))

  return [ x ].concat(input)
}

import { prepend } from './prepend.js'

test('happy', () => {
  expect(prepend('yes', [ 'foo', 'bar', 'baz' ])).toEqual([
    'yes',
    'foo',
    'bar',
    'baz',
  ])
})

test('with empty list', () => {
  expect(prepend('foo')([])).toEqual([ 'foo' ])
})

test('with string instead of array', () => {
  expect(prepend('foo')('bar')).toEqual([ 'foo', 'b', 'a', 'r' ])
})

prevIndex

prevIndex(index: number, list: any[]): number

It returns the next index of the list when the order is descending.

If we have reached the beginning of the list, then it will return the last index of the list.

:boom: Unlike R.nextIndex, which safeguards against index out of bounds, this method does not.

const list = [1, 2, 3]

const result = [
  R.prevIndex(0, list),
  R.prevIndex(1, list),
  R.prevIndex(2, list),
]
// => [2, 0, 1]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.prevIndex(0%2C%20list)%2C%0A%20%20R.prevIndex(1%2C%20list)%2C%0A%20%20R.prevIndex(2%2C%20list)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B2%2C%200%2C%201%5D">Try this <strong>R.prevIndex</strong> example in Rambda REPL</a>

export function prevIndex(index, list){
  return index === 0 ? list.length - 1 : index - 1
}

import { prevIndex } from './prevIndex.js'

const list = [ 1, 2, 3, 4 ]

test('happy path 1', () => {
  expect(prevIndex(2, list)).toBe(1)
})

test('happy path 2', () => {
  expect(prevIndex(0, list)).toBe(3)
})

produce

produce<Input extends any, Output>(
  rules: ProduceRules<Output, keyof Output, Input>,
  input: Input
): Output

It returns an object created by applying each value of rules to input argument.

:boom: In Typescript context, rules functions can be only 1 level deep. In Javascript context, there is no such restriction.

const rules = {
  foo: R.pipe(R.add(1), R.add(2)),
  a: {b: R.add(3)}
}
const result = R.produce(rules, 1)

const expected = {
  foo: 4,
  a: {b: 4}
}
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20rules%20%3D%20%7B%0A%20%20foo%3A%20R.pipe(R.add(1)%2C%20R.add(2))%2C%0A%20%20a%3A%20%7Bb%3A%20R.add(3)%7D%0A%7D%0Aconst%20result%20%3D%20R.produce(rules%2C%201)%0A%0Aconst%20expected%20%3D%20%7B%0A%20%20foo%3A%204%2C%0A%20%20a%3A%20%7Bb%3A%204%7D%0A%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.produce</strong> example in Rambda REPL</a>

import { map } from './map.js'
import { type } from './type.js'

export function produce(rules, input){
  if (arguments.length === 1){
    return _input => produce(rules, _input)
  }

  return map(singleRule =>
    type(singleRule) === 'Object' ?
      produce(singleRule, input) :
      singleRule(input),
  rules)
}

import { add, pipe } from '../rambda.js'
import { produce } from './produce.js'

const rules = {
  a : pipe(add(2), add(3)),
  b : x => ({ foo : x }),
  c : {
    d : add(2),
    e : add(10),
  },
}

const expected = {
  a : 6,
  b : { foo : 1 },
  c : {
    d : 3,
    e : 11,
  },
}

test('happy', () => {
  const result = produce(rules, 1)
  expect(result).toEqual(expected)
})

test('curried', () => {
  const result = produce(rules)(1)
  expect(result).toEqual(expected)
})

produceAsync

produceAsync<Input extends any, Output>(
  rules: ProduceAsyncRules<Output, keyof Output, Input>,
  input: Input
): Promise<Output>

It returns an object created by applying each value of rules to input argument.

rules input is an object with synchronous or asynchronous functions as values.

The return value is wrapped in a promise, even if all rules are synchronous functions.

const rules = {
  foo: async x => {
    await R.delay(100)
    return x > 1
  },
  bar: x => ({baz: x})
}
const input = 2
const result = await R.produceAsync(rules, input)

const expected = {
  foo: true,
  bar: {baz: 2}
}
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20rules%20%3D%20%7B%0A%20%20foo%3A%20async%20x%20%3D%3E%20%7B%0A%20%20%20%20await%20R.delay(100)%0A%20%20%20%20return%20x%20%3E%201%0A%20%20%7D%2C%0A%20%20bar%3A%20x%20%3D%3E%20(%7Bbaz%3A%20x%7D)%0A%7D%0Aconst%20input%20%3D%202%0Aconst%20result%20%3D%20await%20R.produceAsync(rules%2C%20input)%0A%0Aconst%20expected%20%3D%20%7B%0A%20%20foo%3A%20true%2C%0A%20%20bar%3A%20%7Bbaz%3A%202%7D%0A%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.produceAsync</strong> example in Rambda REPL</a>

import { map } from './map.js'
import { type } from './type.js'

function promisify({ condition, input, prop }){
  return new Promise((resolve, reject) => {
    if (type(condition) !== 'Promise'){
      return resolve({
        type    : prop,
        payload : condition(input),
      })
    }

    condition(input)
      .then(result => {
        resolve({
          type    : prop,
          payload : result,
        })
      })
      .catch(err => reject(err))
  })
}

function produceFn(conditions, input){
  let asyncConditionsFlag = false
  for (const prop in conditions){
    if (
      asyncConditionsFlag === false &&
      type(conditions[ prop ]) === 'Promise'
    ){
      asyncConditionsFlag = true
    }
  }

  if (asyncConditionsFlag === false){
    const willReturn = {}
    for (const prop in conditions){
      willReturn[ prop ] = conditions[ prop ](input)
    }

    return Promise.resolve(willReturn)
  }

  const promised = []
  for (const prop in conditions){
    const condition = conditions[ prop ]
    promised.push(promisify({
      input,
      condition,
      prop,
    }))
  }

  return new Promise((resolve, reject) => {
    Promise.all(promised)
      .then(results => {
        const willReturn = {}

        map(result => willReturn[ result.type ] = result.payload, results)

        resolve(willReturn)
      })
      .catch(err => reject(err))
  })
}

export function produceAsync(conditions, input){
  if (arguments.length === 1){
    return async _input => produceFn(conditions, _input)
  }

  return new Promise((resolve, reject) => {
    produceFn(conditions, input).then(resolve)
      .catch(reject)
  })
}

import { delay } from './delay.js'
import { produceAsync } from './produceAsync.js'

test('happy', async () => {
  const result = await produceAsync({
    foo : async x => {
      await delay(100)

      return `${ x }_ZEPPELIN`
    },
    bar : x => x.length === 3,
  },
  'LED')
  const expected = {
    foo : 'LED_ZEPPELIN',
    bar : true,
  }

  expect(result).toEqual(expected)
})

test('when all rules are synchronous', async () => {
  const result = await produceAsync({
    foo : x => `${ x }_ZEPPELIN`,
    bar : x => x.length === 3,
  },
  'LED')
  const expected = {
    foo : 'LED_ZEPPELIN',
    bar : true,
  }

  expect(result).toEqual(expected)
})

test('with error', async () => {
  const fn = produceAsync({
    foo : async x => {
      await delay(100)
      throw new Error(`${ x }_ZEPPELIN`)
    },
    bar : inputArgument => inputArgument === 5,
  })

  await expect(fn('LED')).rejects.toThrow('LED_ZEPPELIN')
})

product

product(list: number[]): number

R.product([ 2, 3, 4 ])
// => 24)

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.product(%5B%202%2C%203%2C%204%20%5D)%0A%2F%2F%20%3D%3E%2024)">Try this <strong>R.product</strong> example in Rambda REPL</a>

import { multiply } from './multiply.js'
import { reduce } from './reduce.js'

export const product = reduce(multiply, 1)

import { product } from './product.js'

test('happy', () => {
  expect(product([ 2, 3, 4 ])).toBe(24)
})

test('bad input', () => {
  expect(product([ null ])).toBe(0)
  expect(product([])).toBe(1)
})

prop

prop<_, P extends keyof never, T>(p: P, value: T): Prop<T, P>

It returns the value of property propToFind in obj.

If there is no such property, it returns undefined.

const result = [
  R.prop('x', {x: 100}), 
  R.prop('x', {a: 1}) 
]
// => [100, undefined]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.prop('x'%2C%20%7Bx%3A%20100%7D)%2C%20%0A%20%20R.prop('x'%2C%20%7Ba%3A%201%7D)%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B100%2C%20undefined%5D">Try this <strong>R.prop</strong> example in Rambda REPL</a>

export function propFn(searchProperty, obj){
  if (!obj) return undefined

  return obj[ searchProperty ]
}

export function prop(searchProperty, obj){
  if (arguments.length === 1) return _obj => prop(searchProperty, _obj)

  return propFn(searchProperty, obj)
}

import { prop } from './prop.js'

test('prop', () => {
  expect(prop('foo')({ foo : 'baz' })).toBe('baz')

  expect(prop('bar')({ foo : 'baz' })).toBeUndefined()

  expect(prop('bar')(null)).toBeUndefined()
})

propEq

propEq<K extends string | number>(valueToMatch: any, propToFind: K, obj: Record<K, any>): boolean

It returns true if obj has property propToFind and its value is equal to valueToMatch.

const obj = { foo: 'bar' }
const secondObj = { foo: 1 }

const propToFind = 'foo'
const valueToMatch = 'bar'

const result = [
  R.propEq(propToFind, valueToMatch, Record<string, unknown>),
  R.propEq(propToFind, valueToMatch, secondRecord<string, unknown>)
]
// => [true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%20foo%3A%20'bar'%20%7D%0Aconst%20secondObj%20%3D%20%7B%20foo%3A%201%20%7D%0A%0Aconst%20propToFind%20%3D%20'foo'%0Aconst%20valueToMatch%20%3D%20'bar'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.propEq(propToFind%2C%20valueToMatch%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propEq(propToFind%2C%20valueToMatch%2C%20secondRecord%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.propEq</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { equals } from './equals.js'
import { prop } from './prop.js'

function propEqFn(
  valueToMatch, propToFind, obj
){
  if (!obj) return false

  return equals(valueToMatch, prop(propToFind, obj))
}

export const propEq = curry(propEqFn)

import { BAR, FOO } from './_internals/testUtils.js'
import { propEq } from './propEq.js'

test('happy', () => {
  const obj = { [ FOO ] : BAR }
  expect(propEq(BAR, FOO)(obj)).toBeTrue()
  expect(propEq(1, FOO)(obj)).toBeFalse()
  expect(propEq(1)(FOO)(obj)).toBeFalse()
  expect(propEq(
    1, 1, null
  )).toBeFalse()
})

test('returns false if called with a null or undefined object', () => {
  expect(propEq(
    'name', 'Abby', null
  )).toBeFalse()
  expect(propEq(
    'name', 'Abby', undefined
  )).toBeFalse()
})

propIs

propIs<C extends AnyFunction, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>

It returns true if property of obj is from target type.

const obj = {a:1, b: 'foo'}

const result = [
  R.propIs(Number, 'a', Record<string, unknown>),
  R.propIs(String, 'b', Record<string, unknown>),
  R.propIs(Number, 'b', Record<string, unknown>),
]
// => [true, true, false]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A1%2C%20b%3A%20'foo'%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.propIs(Number%2C%20'a'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propIs(String%2C%20'b'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propIs(Number%2C%20'b'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.propIs</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { is } from './is.js'

function propIsFn(
  targetPrototype, property, obj
){
  return is(targetPrototype, obj[ property ])
}

export const propIs = curry(propIsFn)

import { propIs } from './propIs.js'

const obj = {
  a : 1,
  b : 'foo',
}

test('when true', () => {
  expect(propIs(
    Number, 'a', obj
  )).toBeTrue()
  expect(propIs(
    String, 'b', obj
  )).toBeTrue()
})

test('when false', () => {
  expect(propIs(
    String, 'a', obj
  )).toBeFalse()
  expect(propIs(
    Number, 'b', obj
  )).toBeFalse()
})

propOr

propOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T

It returns either defaultValue or the value of property in obj.

const obj = {a: 1}
const defaultValue = 'DEFAULT_VALUE'
const property = 'a'

const result = [
  R.propOr(defaultValue, property, Record<string, unknown>),
  R.propOr(defaultValue, 'foo', Record<string, unknown>)
]
// => [1, 'DEFAULT_VALUE']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%7D%0Aconst%20defaultValue%20%3D%20'DEFAULT_VALUE'%0Aconst%20property%20%3D%20'a'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.propOr(defaultValue%2C%20property%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propOr(defaultValue%2C%20'foo'%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%20'DEFAULT_VALUE'%5D">Try this <strong>R.propOr</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { defaultTo } from './defaultTo.js'

function propOrFn(
  defaultValue, property, obj
){
  if (!obj) return defaultValue

  return defaultTo(defaultValue, obj[ property ])
}

export const propOr = curry(propOrFn)

import { propOr } from './propOr.js'

test('propOr (result)', () => {
  const obj = { a : 1 }
  expect(propOr(
    'default', 'a', obj
  )).toBe(1)
  expect(propOr(
    'default', 'notExist', obj
  )).toBe('default')
  expect(propOr(
    'default', 'notExist', null
  )).toBe('default')
})

test('propOr (currying)', () => {
  const obj = { a : 1 }
  expect(propOr('default')('a', obj)).toBe(1)
  expect(propOr('default', 'a')(obj)).toBe(1)
  expect(propOr('default')('notExist', obj)).toBe('default')
  expect(propOr('default', 'notExist')(obj)).toBe('default')
})

props

props<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[]

It takes list with properties propsToPick and returns a list with property values in obj.

const result = R.props(
  ['a', 'b'], 
  {a:1, c:3}
)
// => [1, undefined]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.props(%0A%20%20%5B'a'%2C%20'b'%5D%2C%20%0A%20%20%7Ba%3A1%2C%20c%3A3%7D%0A)%0A%2F%2F%20%3D%3E%20%5B1%2C%20undefined%5D">Try this <strong>R.props</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { mapArray } from './map.js'

export function props(propsToPick, obj){
  if (arguments.length === 1){
    return _obj => props(propsToPick, _obj)
  }
  if (!isArray(propsToPick)){
    throw new Error('propsToPick is not a list')
  }

  return mapArray(prop => obj[ prop ], propsToPick)
}

import { props } from './props.js'

const obj = {
  a : 1,
  b : 2,
}
const propsToPick = [ 'a', 'c' ]

test('happy', () => {
  const result = props(propsToPick, obj)
  expect(result).toEqual([ 1, undefined ])
})

test('curried', () => {
  const result = props(propsToPick)(obj)
  expect(result).toEqual([ 1, undefined ])
})

test('wrong input', () => {
  expect(() => props(null)(obj)).toThrowErrorMatchingInlineSnapshot('"propsToPick is not a list"')
})

propSatisfies

propSatisfies<T>(predicate: Predicate<T>, property: string, obj: Record<string, T>): boolean

It returns true if the object property satisfies a given predicate.

const obj = {a: {b:1}}
const property = 'a'
const predicate = x => x?.b === 1

const result = R.propSatisfies(predicate, property, Record<string, unknown>)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%20%7Bb%3A1%7D%7D%0Aconst%20property%20%3D%20'a'%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%3F.b%20%3D%3D%3D%201%0A%0Aconst%20result%20%3D%20R.propSatisfies(predicate%2C%20property%2C%20Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.propSatisfies</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { prop } from './prop.js'

function propSatisfiesFn(
  predicate, property, obj
){
  return predicate(prop(property, obj))
}

export const propSatisfies = curry(propSatisfiesFn)

import { propSatisfies } from './propSatisfies.js'

const obj = { a : 1 }

test('when true', () => {
  expect(propSatisfies(
    x => x > 0, 'a', obj
  )).toBeTrue()
})

test('when false', () => {
  expect(propSatisfies(x => x < 0, 'a')(obj)).toBeFalse()
})

random

random(minInclusive: number, maxInclusive: number): number

It returns a random number between min inclusive and max inclusive.

export function random(min, max){
  return Math.floor(Math.random() * (max - min + 1)) + min
}

import { random } from './random.js'
import { range } from './range.js'

test('when returns true', () => {
  range(0, 100).map(() => {
    const randomResult = random(1, 10)
    expect(randomResult).toBeLessThanOrEqual(10)
    expect(randomResult).toBeGreaterThanOrEqual(1)
  })
})

range

range(startInclusive: number, endExclusive: number): number[]

It returns list of numbers between startInclusive to endExclusive markers.

R.range(0, 5)
// => [0, 1, 2, 3, 4]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.range(0%2C%205)%0A%2F%2F%20%3D%3E%20%5B0%2C%201%2C%202%2C%203%2C%204%5D">Try this <strong>R.range</strong> example in Rambda REPL</a>

export function range(start, end){
  if (arguments.length === 1) return _end => range(start, _end)

  if (Number.isNaN(Number(start)) || Number.isNaN(Number(end))){
    throw new TypeError('Both arguments to range must be numbers')
  }

  if (end < start) return []

  const len = end - start
  const willReturn = Array(len)

  for (let i = 0; i < len; i++){
    willReturn[ i ] = start + i
  }

  return willReturn
}

import { range } from './range.js'

test('happy', () => {
  expect(range(0, 10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

test('end range is bigger than start range', () => {
  expect(range(7, 3)).toEqual([])
  expect(range(5, 5)).toEqual([])
})

test('with bad input', () => {
  const throwMessage = 'Both arguments to range must be numbers'
  expect(() => range('a', 6)).toThrowWithMessage(Error, throwMessage)
  expect(() => range(6, 'z')).toThrowWithMessage(Error, throwMessage)
})

test('curry', () => {
  expect(range(0)(10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})

reduce

:boom: It passes index of the list as third argument to reducer function.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20initialValue%20%3D%2010%0Aconst%20reducer%20%3D%20(prev%2C%20current)%20%3D%3E%20prev%20*%20current%0A%0Aconst%20result%20%3D%20R.reduce(reducer%2C%20initialValue%2C%20list)%0A%2F%2F%20%3D%3E%2060">Try this <strong>R.reduce</strong> example in Rambda REPL</a>

reduceBy

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.reduceBy(%0A%20%20(acc%2C%20elem)%20%3D%3E%20acc%20%2B%20elem%2C%0A%20%200%2C%0A%20%20x%20%3D%3E%20x%20%3E%202%20%3F%20'big'%20%3A%20'small'%2C%0A%20%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0A)%0A%2F%2F%20%3D%3E%20%7B%20big%3A%2012%2C%20small%3A%203%20%7D">Try this <strong>R.reduceBy</strong> example in Rambda REPL</a>

reject

reject<T>(predicate: Predicate<T>, list: T[]): T[]

It has the opposite effect of R.filter.

const list = [1, 2, 3, 4]
const obj = {a: 1, b: 2}
const predicate = x => x > 1

const result = [
  R.reject(predicate, list),
  R.reject(predicate, Record<string, unknown>)
]
// => [[1], {a: 1}]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%201%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.reject(predicate%2C%20list)%2C%0A%20%20R.reject(predicate%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B1%5D%2C%20%7Ba%3A%201%7D%5D">Try this <strong>R.reject</strong> example in Rambda REPL</a>

import { filter } from './filter.js'

export function reject(predicate, list){
  if (arguments.length === 1) return _list => reject(predicate, _list)

  return filter(x => !predicate(x), list)
}

import { reject } from './reject.js'

const isOdd = n => n % 2 === 1

test('with array', () => {
  expect(reject(isOdd)([ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
})

test('with object', () => {
  const obj = {
    a : 1,
    b : 2,
    c : 3,
    d : 4,
  }
  expect(reject(isOdd, obj)).toEqual({
    b : 2,
    d : 4,
  })
})

rejectIndexed

Same as R.reject, but it passes index/property as second argument to the predicate, when looping over arrays/objects.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.reject((x%2C%20index)%20%3D%3E%20x%20%3E%201%2C%20list)%0A%20%20R.reject((x%2C%20property)%20%3D%3E%20x%20%3E%201%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B1%5D%2C%20%7Ba%3A%201%7D%5D">Try this <strong>R.rejectIndexed</strong> example in Rambda REPL</a>

remove

It will remove all toRemove entries from text sequentially.

toRemove argument can be either a list of strings/regular expressions or a single string/regular expression.

:boom: This is the only case where Rambdax exports clashes with Ramda API, as Ramda has remove method. If Rambda.remove is introduced, then this method will be renamed.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.remove(%0A%20%20%5B'foo'%2C'bar'%5D%2C%0A%20%20'foo%20bar%20baz%20foo'%0A)%0A%2F%2F%20%3D%3E%20'baz%20foo'">Try this <strong>R.remove</strong> example in Rambda REPL</a>

removeIndex

removeIndex<T>(index: number, list: T[]): T[]

It returns a copy of list input with removed index.

const list = [1, 2, 3, 4]
const result = R.removeIndex(1, list)
// => [1, 3, 4]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20result%20%3D%20R.removeIndex(1%2C%20list)%0A%2F%2F%20%3D%3E%20%5B1%2C%203%2C%204%5D">Try this <strong>R.removeIndex</strong> example in Rambda REPL</a>

export function removeIndex(index, list){
  if (arguments.length === 1) return _list => removeIndex(index, _list)
  if (index <= 0) return list.slice(1)
  if (index >= list.length - 1) return list.slice(0, list.length - 1)

  return [ ...list.slice(0, index), ...list.slice(index + 1) ]
}

import { removeIndex } from './removeIndex.js'

const list = [ 1, 2, 3, 4 ]

test('first or before first index', () => {
  expect(removeIndex(-2, list)).toEqual([ 2, 3, 4 ])
  expect(removeIndex(-2)(list)).toEqual([ 2, 3, 4 ])
})

test('last or after last index', () => {
  expect(removeIndex(4, list)).toEqual([ 1, 2, 3 ])
  expect(removeIndex(10, list)).toEqual([ 1, 2, 3 ])
})

test('middle index', () => {
  expect(removeIndex(1, list)).toEqual([ 1, 3, 4 ])
  expect(removeIndex(2, list)).toEqual([ 1, 2, 4 ])
})

renameProps

renameProps(rules: object, input: object): object

If property prop of rules is also a property in input, then rename input property to rules[prop].

import { mergeRight } from './mergeRight.js'
import { omit } from './omit.js'

export function renameProps(conditions, inputObject){
  if (arguments.length === 1){
    return inputObjectHolder => renameProps(conditions, inputObjectHolder)
  }
  const renamed = {}
  Object.keys(conditions).forEach(condition => {
    if (Object.keys(inputObject).includes(condition)){
      renamed[ conditions[ condition ] ] = inputObject[ condition ]
    }
  })

  return mergeRight(renamed, omit(Object.keys(conditions), inputObject))
}

import { renameProps } from './renameProps.js'

test('renameProps', () => {
  const rules = {
    f : 'foo',
    b : 'bar',
    q : 'x',
  }
  const input = {
    f : 1,
    b : 2,
    a : 3,
  }
  const result = renameProps(rules, input)
  const expectedResult = {
    foo : 1,
    bar : 2,
    a   : 3,
  }
  expect(result).toEqual(expectedResult)
})

test('curry', () => {
  const rules = {
    f : 'foo',
    b : 'bar',
  }
  const input = {
    f : 1,
    b : 2,
  }
  const result = renameProps(rules)(input)
  const expectedResult = {
    foo : 1,
    bar : 2,
  }
  expect(result).toEqual(expectedResult)
})

repeat

repeat<T>(x: T): (timesToRepeat: number) => T[]

R.repeat('foo', 3)
// => ['foo', 'foo', 'foo']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.repeat('foo'%2C%203)%0A%2F%2F%20%3D%3E%20%5B'foo'%2C%20'foo'%2C%20'foo'%5D">Try this <strong>R.repeat</strong> example in Rambda REPL</a>

export function repeat(x, timesToRepeat){
  if (arguments.length === 1){
    return _timesToRepeat => repeat(x, _timesToRepeat)
  }

  return Array(timesToRepeat).fill(x)
}

import { repeat } from './repeat.js'

test('repeat', () => {
  expect(repeat('')(3)).toEqual([ '', '', '' ])
  expect(repeat('foo', 3)).toEqual([ 'foo', 'foo', 'foo' ])

  const obj = {}
  const arr = repeat(obj, 3)

  expect(arr).toEqual([ {}, {}, {} ])

  expect(arr[ 0 ] === arr[ 1 ]).toBeTrue()
})

replace

replace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string

It replaces strOrRegex found in str with replacer.

const strOrRegex = /o/g

const result = R.replace(strOrRegex, '|0|', 'foo')
// => 'f|0||0|'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20strOrRegex%20%3D%20%2Fo%2Fg%0A%0Aconst%20result%20%3D%20R.replace(strOrRegex%2C%20'%7C0%7C'%2C%20'foo')%0A%2F%2F%20%3D%3E%20'f%7C0%7C%7C0%7C'">Try this <strong>R.replace</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

function replaceFn(
  pattern, replacer, str
){
  return str.replace(pattern, replacer)
}

export const replace = curry(replaceFn)

import { replace } from './replace.js'

test('happy', () => {
  expect(replace(
    /\s/g, '|', 'foo bar baz'
  )).toBe('foo|bar|baz')
})

test('with function as replacer input', () => {
  expect(replace(
    /\s/g,
    (
      match, offset, str
    ) => {
      expect(match).toBe(' ')
      expect([ 3, 7 ].includes(offset)).toBeTrue()
      expect(str).toBe('foo bar baz')

      return '|'
    },
    'foo bar baz'
  )).toBe('foo|bar|baz')
})

replaceAll

replaceAll(patterns: (RegExp | string)[], replacer: string, input: string): string

Same as R.replace but it accepts array of string and regular expressions instead of a single value.

const replacer = '|'
const patterns = [ /foo/g, 'bar' ]
const input = 'foo bar baz foo bar'

const result = R.replaceAll(patterns, replacer, input)
// => '| | baz | bar'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20replacer%20%3D%20'%7C'%0Aconst%20patterns%20%3D%20%5B%20%2Ffoo%2Fg%2C%20'bar'%20%5D%0Aconst%20input%20%3D%20'foo%20bar%20baz%20foo%20bar'%0A%0Aconst%20result%20%3D%20R.replaceAll(patterns%2C%20replacer%2C%20input)%0A%2F%2F%20%3D%3E%20'%7C%20%7C%20baz%20%7C%20bar'">Try this <strong>R.replaceAll</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { ok } from './ok.js'

function replaceAllFn(
  patterns, replacer, input
){
  ok(
    patterns, replacer, input
  )(
    Array, String, String
  )

  let text = input
  patterns.forEach(singlePattern => {
    text = text.replace(singlePattern, replacer)
  })

  return text
}

export const replaceAll = curry(replaceAllFn)

import {replaceAll} from './replaceAll.js'

const replacer = '|'
const patterns = [/foo/g, 'bar']
const input = 'foo bar baz foo bar'

test('happy', () => {
  const result = replaceAll(patterns, replacer, input)
  const expected = '| | baz | bar'

  expect(result).toEqual(expected)
})

test('throws when wrong patterns', () => {
  expect(() => replaceAll({}, replacer, input))
    .toThrowErrorMatchingInlineSnapshot(`
    "Failed R.ok -
    reason: {"input":{},"schema":"array"}
    all inputs: [{},"|","foo bar baz foo bar"]
    all schemas: ["array","string","string"]"
  `)
})

test('throws when wrong input', () => {
  expect(() => replaceAll(patterns, replacer, []))
    .toThrowErrorMatchingInlineSnapshot(`
    "Failed R.ok -
    reason: {"input":[],"schema":"string"}
    all inputs: [[{},"bar"],"|",[]]
    all schemas: ["array","string","string"]"
  `)
})

test('throws when wrong replacer', () => {
  expect(() => replaceAll(patterns, null, input))
    .toThrowErrorMatchingInlineSnapshot(`
    "Failed R.ok -
    reason: {"input":null,"schema":"string"}
    all inputs: [[{},"bar"],null,"foo bar baz foo bar"]
    all schemas: ["array","string","string"]"
  `)
})

reset

reset(): void

:boom: R.getter method contains explanations, tests and source information of R.reset, R.setter and R.getter methods.

reverse

reverse<T>(input: T[]): T[]

It returns a reversed copy of list or string input.

const result = [
  R.reverse('foo'),
  R.reverse([1, 2, 3])
]
// => ['oof', [3, 2, 1]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.reverse('foo')%2C%0A%20%20R.reverse(%5B1%2C%202%2C%203%5D)%0A%5D%0A%2F%2F%20%3D%3E%20%5B'oof'%2C%20%5B3%2C%202%2C%201%5D">Try this <strong>R.reverse</strong> example in Rambda REPL</a>

export function reverse(listOrString) {
  if (typeof listOrString === 'string') {
    return listOrString.split('').reverse().join('')
  }

  const clone = listOrString.slice()

  return clone.reverse()
}

import {reverse} from './reverse.js'

test('happy', () => {
  expect(reverse([1, 2, 3])).toEqual([3, 2, 1])
})

test('with string', () => {
  expect(reverse('baz')).toBe('zab')
})

test("it doesn't mutate", () => {
  const arr = [1, 2, 3]

  expect(reverse(arr)).toEqual([3, 2, 1])

  expect(arr).toEqual([1, 2, 3])
})

set

set<S, A>(lens: Lens<S, A>): {
  (a: A): (obj: S) => S
  (a: A, obj: S): S
}

It returns a copied Object or Array with modified lens focus set to replacer value.

const input = {x: 1, y: 2}
const xLens = R.lensProp('x')

const result = [
  R.set(xLens, 4, input),
  R.set(xLens, 8, input) 
]
// => [{x: 4, y: 2}, {x: 8, y: 2}]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20input%20%3D%20%7Bx%3A%201%2C%20y%3A%202%7D%0Aconst%20xLens%20%3D%20R.lensProp('x')%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.set(xLens%2C%204%2C%20input)%2C%0A%20%20R.set(xLens%2C%208%2C%20input)%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B%7Bx%3A%204%2C%20y%3A%202%7D%2C%20%7Bx%3A%208%2C%20y%3A%202%7D%5D">Try this <strong>R.set</strong> example in Rambda REPL</a>

import {always} from './always.js'
import {curry} from './curry.js'
import {over} from './over.js'

function setFn(lens, replacer, x) {
  return over(lens, always(replacer), x)
}

export const set = curry(setFn)

import {assoc} from './assoc.js'
import {lens} from './lens.js'
import {lensIndex} from './lensIndex.js'
import {lensPath} from './lensPath.js'
import {prop} from './prop.js'
import {set} from './set.js'

const testObject = {
  foo: 'bar',
  baz: {
    a: 'x',
    b: 'y',
  },
}

test('assoc lens', () => {
  const assocLens = lens(prop('foo'), assoc('foo'))
  const result = set(assocLens, 'FOO', testObject)
  const expected = {
    ...testObject,
    foo: 'FOO',
  }
  expect(result).toEqual(expected)
})

test('path lens', () => {
  const pathLens = lensPath('baz.a')
  const result = set(pathLens, 'z', testObject)
  const expected = {
    ...testObject,
    baz: {
      a: 'z',
      b: 'y',
    },
  }
  expect(result).toEqual(expected)
})

test('index lens', () => {
  const indexLens = lensIndex(0)

  const result = set(indexLens, 3, [1, 2])
  expect(result).toEqual([3, 2])
})

setter

setter(keyOrObject: string | object, value?: any): void

:boom: R.getter method contains explanations, tests and source information of R.reset, R.setter and R.getter methods.

shuffle

shuffle<T>(list: T[]): T[]

It returns a randomized copy of array.

export function shuffle(arrayRaw){
  const array = arrayRaw.concat()
  let counter = array.length
  while (counter > 0){
    const index = Math.floor(Math.random() * counter)
    counter--
    const temp = array[ counter ]
    array[ counter ] = array[ index ]
    array[ index ] = temp
  }

  return array
}

import { range } from './range.js'
import { shuffle } from './shuffle.js'
import { uniq } from './uniq.js'

test('happy', () => {
  const list = range(0, 7)
  const result = range(0, 300).map(() => shuffle(list))
  const allUniq = uniq(result)
  expect(allUniq.length > 150).toBeTrue()
})

slice

slice(from: number, to: number, input: string): string

const list = [0, 1, 2, 3, 4, 5]
const str = 'FOO_BAR'
const from = 1
const to = 4

const result = [
  R.slice(from, to, str),
  R.slice(from, to, list)
]
// => ['OO_', [1, 2, 3]]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B0%2C%201%2C%202%2C%203%2C%204%2C%205%5D%0Aconst%20str%20%3D%20'FOO_BAR'%0Aconst%20from%20%3D%201%0Aconst%20to%20%3D%204%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.slice(from%2C%20to%2C%20str)%2C%0A%20%20R.slice(from%2C%20to%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5B'OO_'%2C%20%5B1%2C%202%2C%203%5D%5D">Try this <strong>R.slice</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

function sliceFn(
  from, to, list
){
  return list.slice(from, to)
}

export const slice = curry(sliceFn)

import { slice } from './slice.js'

test('slice', () => {
  expect(slice(
    1, 3, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    1, Infinity, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c', 'd' ])
  expect(slice(
    0, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'a', 'b', 'c' ])
  expect(slice(
    -3, -1, [ 'a', 'b', 'c', 'd' ]
  )).toEqual([ 'b', 'c' ])
  expect(slice(
    0, 3, 'ramda'
  )).toBe('ram')
})

sort

sort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[]

It returns copy of list sorted by sortFn function, where sortFn needs to return only -1, 0 or 1.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = (x, y) => {
  return x.a > y.a ? 1 : -1
}

const result = R.sort(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%2C%0A%20%20%7Ba%3A%201%7D%0A%5D%0Aconst%20sortFn%20%3D%20(x%2C%20y)%20%3D%3E%20%7B%0A%20%20return%20x.a%20%3E%20y.a%20%3F%201%20%3A%20-1%0A%7D%0A%0Aconst%20result%20%3D%20R.sort(sortFn%2C%20list)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%201%7D%2C%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sort</strong> example in Rambda REPL</a>

import { cloneList } from './_internals/cloneList.js'

export function sort(sortFn, list){
  if (arguments.length === 1) return _list => sort(sortFn, _list)

  return cloneList(list).sort(sortFn)
}

import { sort } from './sort.js'

const fn = (a, b) => a > b ? 1 : -1

test('sort', () => {
  expect(sort((a, b) => a - b)([ 2, 3, 1 ])).toEqual([ 1, 2, 3 ])
})

test('it doesn\'t mutate', () => {
  const list = [ 'foo', 'bar', 'baz' ]

  expect(sort(fn, list)).toEqual([ 'bar', 'baz', 'foo' ])

  expect(list[ 0 ]).toBe('foo')
  expect(list[ 1 ]).toBe('bar')
  expect(list[ 2 ]).toBe('baz')
})

sortBy

sortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[]

It returns copy of list sorted by sortFn function, where sortFn function returns a value to compare, i.e. it doesn't need to return only -1, 0 or 1.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = x => x.a

const result = R.sortBy(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%2C%0A%20%20%7Ba%3A%201%7D%0A%5D%0Aconst%20sortFn%20%3D%20x%20%3D%3E%20x.a%0A%0Aconst%20result%20%3D%20R.sortBy(sortFn%2C%20list)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%201%7D%2C%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sortBy</strong> example in Rambda REPL</a>

import { cloneList } from './_internals/cloneList.js'

export function sortBy(sortFn, list){
  if (arguments.length === 1) return _list => sortBy(sortFn, _list)

  const clone = cloneList(list)

  return clone.sort((a, b) => {
    const aSortResult = sortFn(a)
    const bSortResult = sortFn(b)

    if (aSortResult === bSortResult) return 0

    return aSortResult < bSortResult ? -1 : 1
  })
}

import { compose } from './compose.js'
import { prop } from './prop.js'
import { sortBy } from './sortBy.js'
import { toLower } from './toLower.js'

test('happy', () => {
  const input = [ { a : 2 }, { a : 1 }, { a : 1 }, { a : 3 } ]
  const expected = [ { a : 1 }, { a : 1 }, { a : 2 }, { a : 3 } ]

  const result = sortBy(x => x.a)(input)
  expect(result).toEqual(expected)
})

test('with compose', () => {
  const alice = {
    name : 'ALICE',
    age  : 101,
  }
  const bob = {
    name : 'Bob',
    age  : -10,
  }
  const clara = {
    name : 'clara',
    age  : 314.159,
  }
  const people = [ clara, bob, alice ]
  const sortByNameCaseInsensitive = sortBy(compose(toLower, prop('name')))

  expect(sortByNameCaseInsensitive(people)).toEqual([ alice, bob, clara ])
})

sortByPath

sortByPath<T>(sortPath: Path, list: T[]): T[]

It returns copy of list sorted by sortPath value.

As sortPath is passed to R.path, it can be either a string or an array of strings.

const list = [
  {a: {b: 2}},
  {a: {b: 1}},
  {a: {b: 3}}
]
const result = R.sortByPath('a.b', list)
const expected = [
  {a: {b: 1}},
  {a: {b: 2}},
  {a: {b: 3}}
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%20%7Bb%3A%202%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%201%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%203%7D%7D%0A%5D%0Aconst%20result%20%3D%20R.sortByPath('a.b'%2C%20list)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%20%7Bb%3A%201%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%202%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%203%7D%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sortByPath</strong> example in Rambda REPL</a>

import { path } from './path.js'
import { sortBy } from './sortBy.js'

export function sortByPath(sortPath, list){
  if (arguments.length === 1) return _list => sortByPath(sortPath, _list)

  return sortBy(path(sortPath), list)
}

import { sortByPath } from './sortByPath.js'

const list = [ { a : { b : 3 } }, { a : { b : 1 } }, { a : { b : 2 } } ]
const sorted = [ { a : { b : 1 } }, { a : { b : 2 } }, { a : { b : 3 } } ]

test('with string as path', () => {
  expect(sortByPath('a.b', list)).toEqual(sorted)
})

test('with list of strings as path', () => {
  expect(sortByPath([ 'a', 'b' ], list)).toEqual(sorted)
})

test('with string as path - curried', () => {
  expect(sortByPath('a.b')(list)).toEqual(sorted)
})

test('with list of strings as path - curried', () => {
  expect(sortByPath([ 'a', 'b' ])(list)).toEqual(sorted)
})

sortByProps

sortByProps<T>(sortPaths: string[], list: T[]): T[]

It returns sorted copy of list of objects.

Sorting is done using a list of strings, each representing a path. Two members a and b from list can be sorted if both return a value for a given path. If the value is equal, then the next member of sortPaths(if there is such) will be used in order to find difference between a and b.

const list = [
  {a: {b: 2}},
  {a: {b: 1}},
  {a: {b: 3}}
]
const result = R.sortByProps(['a.b'], list)
const expected = [
  {a: {b: 1}},
  {a: {b: 2}},
  {a: {b: 3}}
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%20%7Bb%3A%202%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%201%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%203%7D%7D%0A%5D%0Aconst%20result%20%3D%20R.sortByProps(%5B'a.b'%5D%2C%20list)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%20%7Bb%3A%201%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%202%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%203%7D%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sortByProps</strong> example in Rambda REPL</a>

import { path } from './path.js'

function singleSort(
  a, b, sortPaths
){
  let toReturn = 0
  sortPaths.forEach(singlePath => {
    if (toReturn !== 0) return
    const aResult = path(singlePath, a)
    const bResult = path(singlePath, b)
    if ([ aResult, bResult ].includes(undefined)) return
    if (aResult === bResult) return

    toReturn = aResult > bResult ? 1 : -1
  })

  return toReturn
}

export function sortByProps(sortPaths, list){
  if (arguments.length === 1) return _list => sortByProps(sortPaths, _list)
  const clone = list.slice()

  clone.sort((a, b) => singleSort(
    a, b, sortPaths
  ))

  return clone
}

import { sortByProps } from './sortByProps.js'

const list = [ { a : { b : 3 } }, { a : { b : 2 } }, { a : { b : 1 } } ]
const sorted = [ { a : { b : 1 } }, { a : { b : 2 } }, { a : { b : 3 } } ]

test('wrong paths are ignored', () => {
  expect(sortByProps([ 'foo.bar', 'a.c', 'a.b', 'a.d' ], list)).toEqual(sorted)
})

test('skip sort when path results are equal', () => {
  const input = [
    {
      a : {
        b : 0,
        c : 2,
      },
    },
    {
      a : {
        b : 0,
        c : 1,
      },
    },
  ]
  expect(sortByProps([ 'a.b', 'a.d' ], input)).toEqual(input)
})

test('when list is already sorted', () => {
  const input = [
    {
      a : {
        b : 0,
        c : 1,
      },
    },
    {
      a : {
        b : 0,
        c : 2,
      },
    },
  ]
  expect(sortByProps([ 'a.b', 'a.c' ])(input)).toEqual(input)
})

sortObject

sortObject<T>(predicate: SortObjectPredicate<T>, input: { [key: string]: T }): { [keyOutput: string]: T }

It returns a sorted version of input object.

const predicate = (propA, propB, valueA, valueB) => valueA > valueB ? -1 : 1

const result = R.sortObject(predicate, {a:1, b: 4, c: 2})
// => {b: 4, c: 2, a: 1}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20(propA%2C%20propB%2C%20valueA%2C%20valueB)%20%3D%3E%20valueA%20%3E%20valueB%20%3F%20-1%20%3A%201%0A%0Aconst%20result%20%3D%20R.sortObject(predicate%2C%20%7Ba%3A1%2C%20b%3A%204%2C%20c%3A%202%7D)%0A%2F%2F%20%3D%3E%20%7Bb%3A%204%2C%20c%3A%202%2C%20a%3A%201%7D">Try this <strong>R.sortObject</strong> example in Rambda REPL</a>

import { sort } from './sort.js'

export function sortObject(predicate, obj){
  if (arguments.length === 1){
    return _obj => sortObject(predicate, _obj)
  }
  const keys = Object.keys(obj)
  const sortedKeys = sort((a, b) => predicate(
    a, b, obj[ a ], obj[ b ]
  ), keys)

  const toReturn = {}
  sortedKeys.forEach(singleKey => {
    toReturn[ singleKey ] = obj[ singleKey ]
  })

  return toReturn
}

import { runTests } from 'helpers-fn'

import { allTrue } from './allTrue.js'
import { equals } from './equals.js'
import { sortObject } from './sortObject.js'

const obj = {
  c : 1,
  a : 2,
  b : 3,
}

const predicateA = (
  propA, propB, valueA, valueB
) => propA > propB ? -1 : 1

const expectationA = [ 'c', 'b', 'a' ]

const predicateB = (
  propA, propB, valueA, valueB
) => propA < propB ? -1 : 1
const expectationB = [ 'a', 'b', 'c' ]
const predicateC = (
  propA, propB, valueA, valueB
) =>
  valueA > valueB ? -1 : 1
const expectationC = [ 'b', 'a', 'c' ]

const fn = ([ predicate, expectation ]) => {
  const result = sortObject(predicate, obj)
  const curriedResult = sortObject(predicate)(obj)
  const sortedKeys = Object.keys(result)
  const sortedKeysCurried = Object.keys(curriedResult)
  const isSameObject = equals(obj, result)
  const isSameObjectCurried = equals(obj, curriedResult)

  return allTrue(
    isSameObject,
    isSameObjectCurried,
    equals(sortedKeys, expectation),
    equals(sortedKeysCurried, expectation)
  )
}

const testData = {
  label : 'foo',
  data  : [
    { ok : [ predicateA, expectationA ] },
    { ok : [ predicateB, expectationB ] },
    { ok : [ predicateC, expectationC ] },
  ],
  fn,
}

runTests(testData)

sortWith

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sortWith(%5B%0A%20%20%20%20(a%2C%20b)%20%3D%3E%20a.a%20%3D%3D%3D%20b.a%20%3F%200%20%3A%20a.a%20%3E%20b.a%20%3F%201%20%3A%20-1%2C%0A%20%20%20%20(a%2C%20b)%20%3D%3E%20a.b%20%3D%3D%3D%20b.b%20%3F%200%20%3A%20a.b%20%3E%20b.b%20%3F%201%20%3A%20-1%2C%0A%5D%2C%20%5B%0A%20%20%7Ba%3A%201%2C%20b%3A%202%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%201%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%202%7D%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%201%7D%2C%0A%5D)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%201%2C%20b%3A%201%7D%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%202%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%201%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%202%7D%2C%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sortWith</strong> example in Rambda REPL</a>

split

split(separator: string | RegExp): (str: string) => string[]

Curried version of String.prototype.split

const str = 'foo|bar|baz'
const separator = '|'
const result = R.split(separator, str)
// => [ 'foo', 'bar', 'baz' ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20str%20%3D%20'foo%7Cbar%7Cbaz'%0Aconst%20separator%20%3D%20'%7C'%0Aconst%20result%20%3D%20R.split(separator%2C%20str)%0A%2F%2F%20%3D%3E%20%5B%20'foo'%2C%20'bar'%2C%20'baz'%20%5D">Try this <strong>R.split</strong> example in Rambda REPL</a>

export function split(separator, str){
  if (arguments.length === 1) return _str => split(separator, _str)

  return str.split(separator)
}

import { split } from './split.js'

const str = 'foo|bar|baz'
const splitChar = '|'
const expected = [ 'foo', 'bar', 'baz' ]

test('happy', () => {
  expect(split(splitChar, str)).toEqual(expected)
})

test('curried', () => {
  expect(split(splitChar)(str)).toEqual(expected)
})

splitAt

splitAt<T>(index: number, input: T[]): [T[], T[]]

It splits string or array at a given index.

const list = [ 1, 2, 3 ]
const result = R.splitAt(2, list)
// => [[ 1, 2 ], [ 3 ]]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%201%2C%202%2C%203%20%5D%0Aconst%20result%20%3D%20R.splitAt(2%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%5B%201%2C%202%20%5D%2C%20%5B%203%20%5D%5D">Try this <strong>R.splitAt</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { drop } from './drop.js'
import { maybe } from './maybe.js'
import { take } from './take.js'

export function splitAt(index, input){
  if (arguments.length === 1){
    return _list => splitAt(index, _list)
  }
  if (!input) throw new TypeError(`Cannot read property 'slice' of ${ input }`)

  if (!isArray(input) && typeof input !== 'string') return [ [], [] ]

  const correctIndex = maybe(
    index < 0,
    input.length + index < 0 ? 0 : input.length + index,
    index
  )

  return [ take(correctIndex, input), drop(correctIndex, input) ]
}

import { splitAt as splitAtRamda } from 'ramda'

import { splitAt } from './splitAt.js'

const list = [ 1, 2, 3 ]
const str = 'foo bar'

test('with array', () => {
  const result = splitAt(2, list)
  expect(result).toEqual([ [ 1, 2 ], [ 3 ] ])
})

test('with array - index is negative number', () => {
  const result = splitAt(-6, list)
  expect(result).toEqual([ [], list ])
})

test('with array - index is out of scope', () => {
  const result = splitAt(4, list)
  expect(result).toEqual([ [ 1, 2, 3 ], [] ])
})

test('with string', () => {
  const result = splitAt(4, str)
  expect(result).toEqual([ 'foo ', 'bar' ])
})

test('with string - index is negative number', () => {
  const result = splitAt(-2, str)
  expect(result).toEqual([ 'foo b', 'ar' ])
})

test('with string - index is out of scope', () => {
  const result = splitAt(10, str)
  expect(result).toEqual([ str, '' ])
})

test('with array - index is out of scope', () => {
  const result = splitAt(4)(list)
  expect(result).toEqual([ [ 1, 2, 3 ], [] ])
})

const badInputs = [ 1, true, /foo/g, {} ]
const throwingBadInputs = [ null, undefined ]

test('with bad inputs', () => {
  throwingBadInputs.forEach(badInput => {
    expect(() => splitAt(1, badInput)).toThrowWithMessage(TypeError,
      `Cannot read property 'slice' of ${ badInput }`)
    expect(() => splitAtRamda(1, badInput)).toThrowWithMessage(TypeError,
      `Cannot read properties of ${ badInput } (reading 'slice')`)
  })

  badInputs.forEach(badInput => {
    const result = splitAt(1, badInput)
    const ramdaResult = splitAtRamda(1, badInput)
    expect(result).toEqual(ramdaResult)
  })
})

splitEvery

splitEvery<T>(sliceLength: number, input: T[]): (T[])[]

It splits input into slices of sliceLength.

const result = [
  R.splitEvery(2, [1, 2, 3]), 
  R.splitEvery(3, 'foobar') 
]

const expected = [
  [[1, 2], [3]],
  ['foo', 'bar']
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.splitEvery(2%2C%20%5B1%2C%202%2C%203%5D)%2C%20%0A%20%20R.splitEvery(3%2C%20'foobar')%20%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%20%5B%5B1%2C%202%5D%2C%20%5B3%5D%5D%2C%0A%20%20%5B'foo'%2C%20'bar'%5D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.splitEvery</strong> example in Rambda REPL</a>

export function splitEvery(sliceLength, listOrString){
  if (arguments.length === 1){
    return _listOrString => splitEvery(sliceLength, _listOrString)
  }

  if (sliceLength < 1){
    throw new Error('First argument to splitEvery must be a positive integer')
  }

  const willReturn = []
  let counter = 0

  while (counter < listOrString.length){
    willReturn.push(listOrString.slice(counter, counter += sliceLength))
  }

  return willReturn
}

import { splitEvery } from './splitEvery.js'

test('happy', () => {
  expect(splitEvery(3, [ 1, 2, 3, 4, 5, 6, 7 ])).toEqual([
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7 ],
  ])

  expect(splitEvery(3)('foobarbaz')).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with bad input', () => {
  expect(() =>
    expect(splitEvery(0)('foo')).toEqual([ 'f', 'o', 'o' ])).toThrowErrorMatchingInlineSnapshot('"First argument to splitEvery must be a positive integer"')
})

splitWhen

splitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[]

It splits list to two arrays according to a predicate function.

The first array contains all members of list before predicate returns true.

const list = [1, 2, 1, 2]
const result = R.splitWhen(R.equals(2), list)
// => [[1], [2, 1, 2]]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%201%2C%202%5D%0Aconst%20result%20%3D%20R.splitWhen(R.equals(2)%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%5B1%5D%2C%20%5B2%2C%201%2C%202%5D%5D">Try this <strong>R.splitWhen</strong> example in Rambda REPL</a>

export function splitWhen(predicate, input){
  if (arguments.length === 1){
    return _input => splitWhen(predicate, _input)
  }
  if (!input)
    throw new TypeError(`Cannot read property 'length' of ${ input }`)

  const preFound = []
  const postFound = []
  let found = false
  let counter = -1

  while (counter++ < input.length - 1){
    if (found){
      postFound.push(input[ counter ])
    } else if (predicate(input[ counter ])){
      postFound.push(input[ counter ])
      found = true
    } else {
      preFound.push(input[ counter ])
    }
  }

  return [ preFound, postFound ]
}

import { splitWhen as splitWhenRamda } from 'ramda'

import { equals } from './equals.js'
import { splitWhen } from './splitWhen.js'

const list = [ 1, 2, 1, 2 ]

test('happy', () => {
  const result = splitWhen(equals(2), list)
  expect(result).toEqual([ [ 1 ], [ 2, 1, 2 ] ])
})

test('when predicate returns false', () => {
  const result = splitWhen(equals(3))(list)
  expect(result).toEqual([ list, [] ])
})

const badInputs = [ 1, true, /foo/g, {} ]
const throwingBadInputs = [ null, undefined ]

test('with bad inputs', () => {
  throwingBadInputs.forEach(badInput => {
    expect(() => splitWhen(equals(2), badInput)).toThrowWithMessage(TypeError,
      `Cannot read property 'length' of ${ badInput }`)
    expect(() => splitWhenRamda(equals(2), badInput)).toThrowWithMessage(TypeError,
      `Cannot read properties of ${ badInput } (reading 'length')`)
  })

  badInputs.forEach(badInput => {
    const result = splitWhen(equals(2), badInput)
    const ramdaResult = splitWhenRamda(equals(2), badInput)
    expect(result).toEqual(ramdaResult)
  })
})

startsWith

startsWith<T extends string>(question: T, input: string): boolean

When iterable is a string, then it behaves as String.prototype.startsWith. When iterable is a list, then it uses R.equals to determine if the target list starts in the same way as the given target.

:boom: It doesn't work with arrays unlike its corresponding Ramda method.

const str = 'foo-bar'
const list = [{a:1}, {a:2}, {a:3}]

const result = [
  R.startsWith('foo', str),
  R.startsWith([{a:1}, {a:2}], list)
]
// => [true, true]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20str%20%3D%20'foo-bar'%0Aconst%20list%20%3D%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%2C%20%7Ba%3A3%7D%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.startsWith('foo'%2C%20str)%2C%0A%20%20R.startsWith(%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%5D%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%5D">Try this <strong>R.startsWith</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'

export function startsWith(question, iterable){
  if (arguments.length === 1)
    return _iterable => startsWith(question, _iterable)

  if (typeof iterable === 'string'){
    return iterable.startsWith(question)
  }
  if (!isArray(question)) return false

  let correct = true
  const filtered = question.filter((x, index) => {
    if (!correct) return false
    const result = equals(x, iterable[ index ])
    if (!result) correct = false

    return result
  })

  return filtered.length === question.length
}

import { startsWith as startsWithRamda } from 'ramda'

import { compareCombinations } from './_internals/testUtils.js'
import { possibleIterables, possibleTargets } from './endsWith.spec.js'
import { startsWith } from './startsWith.js'

test('with string', () => {
  expect(startsWith('foo', 'foo-bar')).toBeTrue()
  expect(startsWith('baz')('foo-bar')).toBeFalse()
})

test('use R.equals with array', () => {
  const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
  expect(startsWith({ a : 1 }, list)).toBeFalse()
  expect(startsWith([ { a : 1 } ], list)).toBeTrue()
  expect(startsWith([ { a : 1 }, { a : 2 } ], list)).toBeTrue()
  expect(startsWith(list, list)).toBeTrue()
  expect(startsWith([ { a : 2 } ], list)).toBeFalse()
})

describe('brute force', () => {
  compareCombinations({
    fn          : startsWith,
    fnRamda     : startsWithRamda,
    firstInput  : possibleTargets,
    secondInput : possibleIterables,
    callback    : errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 32,
        }
      `)
    },
  })
})

subtract

Curried version of x - y

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%203%0Aconst%20y%20%3D%201%0A%0Aconst%20result%20%3D%20R.subtract(x%2C%20y)%20%0A%2F%2F%20%3D%3E%202">Try this <strong>R.subtract</strong> example in Rambda REPL</a>

sum

sum(list: number[]): number

R.sum([1, 2, 3, 4, 5]) 
// => 15

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sum(%5B1%2C%202%2C%203%2C%204%2C%205%5D)%20%0A%2F%2F%20%3D%3E%2015">Try this <strong>R.sum</strong> example in Rambda REPL</a>

export function sum(list){
  return list.reduce((prev, current) => prev + current, 0)
}

import { sum } from './sum.js'

test('happy', () => {
  expect(sum([ 1, 2, 3, 4, 5 ])).toBe(15)
})

swap

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.swap(1%2C%202%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%203%2C%202%5D">Try this <strong>R.swap</strong> example in Rambda REPL</a>

switcher

switcher<T>(valueToMatch: any): Switchem<T>

Edited fork of Switchem library.

The method return a value if the matched option is a value.

If the matched option is a function, then R.switcher returns a function which expects input. Tests of the method explain it better than this short description.

R.equals is used to determine equality.

const valueToMatch = {foo: 1}

const result = R.switcher(valueToMatch)
  .is('baz', 'is baz')
  .is(x => typeof x === 'boolean', 'is boolean')
  .is({foo: 1}, 'Property foo is 1')
  .default('is bar')

// => 'Property foo is 1'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20valueToMatch%20%3D%20%7Bfoo%3A%201%7D%0A%0Aconst%20result%20%3D%20R.switcher(valueToMatch)%0A%20%20.is('baz'%2C%20'is%20baz')%0A%20%20.is(x%20%3D%3E%20typeof%20x%20%3D%3D%3D%20'boolean'%2C%20'is%20boolean')%0A%20%20.is(%7Bfoo%3A%201%7D%2C%20'Property%20foo%20is%201')%0A%20%20.default('is%20bar')%0A%0A%2F%2F%20%3D%3E%20'Property%20foo%20is%201'">Try this <strong>R.switcher</strong> example in Rambda REPL</a>

import { equals } from './equals.js'

const NO_MATCH_FOUND = Symbol ? Symbol('NO_MATCH_FOUND') : undefined

const getMatchingKeyValuePair = (
  cases, testValue, defaultValue
) => {
  let iterationValue

  for (let index = 0; index < cases.length; index++){
    iterationValue = cases[ index ].test(testValue)

    if (iterationValue !== NO_MATCH_FOUND){
      return iterationValue
    }
  }

  return defaultValue
}

const isEqual = (testValue, matchValue) => {
  const willReturn =
    typeof testValue === 'function' ?
      testValue(matchValue) :
      equals(testValue, matchValue)

  return willReturn
}

const is = (testValue, matchResult = true) => ({
  key  : testValue,
  test : matchValue =>
    isEqual(testValue, matchValue) ? matchResult : NO_MATCH_FOUND,
})

class Switchem{
  constructor(
    defaultValue, cases, willMatch
  ){
    if (cases === undefined && willMatch === undefined){
      this.cases = []
      this.defaultValue = undefined
      this.willMatch = defaultValue
    } else {
      this.cases = cases
      this.defaultValue = defaultValue
      this.willMatch = willMatch
    }

    return this
  }

  default(defaultValue){
    const holder = new Switchem(
      defaultValue, this.cases, this.willMatch
    )

    return holder.match(this.willMatch)
  }

  is(testValue, matchResult){
    return new Switchem(
      this.defaultValue,
      [ ...this.cases, is(testValue, matchResult) ],
      this.willMatch
    )
  }

  match(matchValue){
    return getMatchingKeyValuePair(
      this.cases, matchValue, this.defaultValue
    )
  }
}

export function switcher(input){
  return new Switchem(input)
}

import { add } from './add.js'
import { switcher } from './switcher.js'
import { tap } from './tap.js'
import { trim } from './trim.js'

test('with undefined', () => {
  const result = switcher(undefined)
    .is(x => x === 0, '0')
    .is(x => x === undefined, 'UNDEFINED')
    .default('3')

  expect(result).toBe('UNDEFINED')
})

test('happy', () => {
  const a = true
  const b = false
  const result = switcher([ a, b ])
    .is([ false, false ], '0')
    .is([ false, true ], '1')
    .is([ true, true ], '2')
    .default('3')

  expect(result).toBe('3')
})

test('can compare objects', () => {
  const result = switcher({ a : 1 })
    .is({ a : 1 }, 'it is object')
    .is('baz', 'it is baz')
    .default('it is default')

  expect(result).toBe('it is object')
})

test('options are mixture of functions and values - input match function', () => {
  const fn = switcher('foo').is('bar', 1)
    .is('foo', add(1))
    .default(1000)

  expect(fn(2)).toBe(3)
})

test('options are mixture of functions and values - input match value', () => {
  const result = switcher('bar').is('bar', 1)
    .is('foo', add(1))
    .default(1000)

  expect(result).toBe(1)
})

test('return function if all options are functions', () => {
  const fn = switcher('foo').is('bar', tap)
    .is('foo', add(1))
    .default(trim)

  expect(fn(2)).toBe(3)
})

const switchFn = input =>
  switcher(input)
    .is(x => x.length && x.length === 7, 'has length of 7')
    .is('baz', 'it is baz')
    .default('it is default')

test('works with function as condition', () => {
  expect(switchFn([ 0, 1, 2, 3, 4, 5, 6 ])).toBe('has length of 7')
})

test('works with string as condition', () => {
  expect(switchFn('baz')).toBe('it is baz')
})

test('fallback to default input when no matches', () => {
  expect(switchFn(1)).toBe('it is default')
})

symmetricDifference

symmetricDifference<T>(x: T[], y: T[]): T[]

It returns a merged list of x and y with all equal elements removed.

R.equals is used to determine equality.

const x = [ 1, 2, 3, 4 ]
const y = [ 3, 4, 5, 6 ]

const result = R.symmetricDifference(x, y)
// => [ 1, 2, 5, 6 ]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%20%5B%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20y%20%3D%20%5B%203%2C%204%2C%205%2C%206%20%5D%0A%0Aconst%20result%20%3D%20R.symmetricDifference(x%2C%20y)%0A%2F%2F%20%3D%3E%20%5B%201%2C%202%2C%205%2C%206%20%5D">Try this <strong>R.symmetricDifference</strong> example in Rambda REPL</a>

import { concat } from './concat.js'
import { filter } from './filter.js'
import { includes } from './includes.js'

export function symmetricDifference(x, y){
  if (arguments.length === 1){
    return _y => symmetricDifference(x, _y)
  }

  return concat(filter(value => !includes(value, y), x),
    filter(value => !includes(value, x), y))
}

import { symmetricDifference } from './symmetricDifference.js'

test('symmetricDifference', () => {
  const list1 = [ 1, 2, 3, 4 ]
  const list2 = [ 3, 4, 5, 6 ]
  expect(symmetricDifference(list1)(list2)).toEqual([ 1, 2, 5, 6 ])

  expect(symmetricDifference([], [])).toEqual([])
})

test('symmetricDifference with objects', () => {
  const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
  const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
  expect(symmetricDifference(list1)(list2)).toEqual([
    { id : 1 },
    { id : 2 },
    { id : 5 },
    { id : 6 },
  ])
})

T

T(): boolean

R.T() 
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.T()%20%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.T</strong> example in Rambda REPL</a>

export function T(){
  return true
}

tail

tail<T extends unknown[]>(input: T): T extends [any, ...infer U] ? U : [...T]

It returns all but the first element of input.

const result = [
  R.tail([1, 2, 3]),  
  R.tail('foo') 
]
// => [[2, 3], 'oo']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.tail(%5B1%2C%202%2C%203%5D)%2C%20%20%0A%20%20R.tail('foo')%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B2%2C%203%5D%2C%20'oo'%5D">Try this <strong>R.tail</strong> example in Rambda REPL</a>

import { drop } from './drop.js'

export function tail(listOrString){
  return drop(1, listOrString)
}

import { tail } from './tail.js'

test('tail', () => {
  expect(tail([ 1, 2, 3 ])).toEqual([ 2, 3 ])
  expect(tail([ 1, 2 ])).toEqual([ 2 ])
  expect(tail([ 1 ])).toEqual([])
  expect(tail([])).toEqual([])

  expect(tail('abc')).toBe('bc')
  expect(tail('ab')).toBe('b')
  expect(tail('a')).toBe('')
  expect(tail('')).toBe('')
})

take

take<T>(howMany: number, input: T[]): T[]

It returns the first howMany elements of input.

const howMany = 2

const result = [
  R.take(howMany, [1, 2, 3]),
  R.take(howMany, 'foobar'),
]
// => [[1, 2], 'fo']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20howMany%20%3D%202%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.take(howMany%2C%20%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.take(howMany%2C%20'foobar')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%202%5D%2C%20'fo'%5D">Try this <strong>R.take</strong> example in Rambda REPL</a>

import baseSlice from './_internals/baseSlice.js'

export function take(howMany, listOrString){
  if (arguments.length === 1)
    return _listOrString => take(howMany, _listOrString)
  if (howMany < 0) return listOrString.slice()
  if (typeof listOrString === 'string') return listOrString.slice(0, howMany)

  return baseSlice(
    listOrString, 0, howMany
  )
}

import { take } from './take.js'

test('happy', () => {
  const arr = [ 'foo', 'bar', 'baz' ]

  expect(take(1, arr)).toEqual([ 'foo' ])

  expect(arr).toEqual([ 'foo', 'bar', 'baz' ])

  expect(take(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar' ])
  expect(take(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
  expect(take(3)('rambda')).toBe('ram')
})

test('with negative index', () => {
  expect(take(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(take(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('with zero index', () => {
  expect(take(0, [ 1, 2, 3 ])).toEqual([])
})

takeLast

takeLast<T>(howMany: number, input: T[]): T[]

It returns the last howMany elements of input.

const howMany = 2

const result = [
  R.takeLast(howMany, [1, 2, 3]),
  R.takeLast(howMany, 'foobar'),
]
// => [[2, 3], 'ar']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20howMany%20%3D%202%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.takeLast(howMany%2C%20%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.takeLast(howMany%2C%20'foobar')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B2%2C%203%5D%2C%20'ar'%5D">Try this <strong>R.takeLast</strong> example in Rambda REPL</a>

import baseSlice from './_internals/baseSlice.js'

export function takeLast(howMany, listOrString){
  if (arguments.length === 1)
    return _listOrString => takeLast(howMany, _listOrString)

  const len = listOrString.length
  if (howMany < 0) return listOrString.slice()
  let numValue = howMany > len ? len : howMany

  if (typeof listOrString === 'string')
    return listOrString.slice(len - numValue)

  numValue = len - numValue

  return baseSlice(
    listOrString, numValue, len
  )
}

import { takeLast } from './takeLast.js'

test('with arrays', () => {
  expect(takeLast(1, [ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])

  expect(takeLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'bar', 'baz' ])

  expect(takeLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])

  expect(takeLast(10, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
})

test('with strings', () => {
  expect(takeLast(3, 'rambda')).toBe('bda')

  expect(takeLast(7, 'rambda')).toBe('rambda')
})

test('with negative index', () => {
  expect(takeLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
  expect(takeLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})

takeLastWhile

takeLastWhile(predicate: (x: string) => boolean, input: string): string

const result = R.takeLastWhile(
  x => x > 2,
  [1, 2, 3, 4]
)
// => [3, 4]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.takeLastWhile(%0A%20%20x%20%3D%3E%20x%20%3E%202%2C%0A%20%20%5B1%2C%202%2C%203%2C%204%5D%0A)%0A%2F%2F%20%3D%3E%20%5B3%2C%204%5D">Try this <strong>R.takeLastWhile</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

export function takeLastWhile(predicate, input){
  if (arguments.length === 1){
    return _input => takeLastWhile(predicate, _input)
  }
  if (input.length === 0) return input

  const toReturn = []
  let counter = input.length

  while (counter){
    const item = input[ --counter ]
    if (!predicate(item)){
      break
    }
    toReturn.push(item)
  }

  return isArray(input) ? toReturn.reverse() : toReturn.reverse().join('')
}

import { takeLastWhile } from './takeLastWhile.js'
const assert = require('assert')

const list = [ 1, 2, 3, 4 ]

test('happy', () => {
  const predicate = x => x > 2
  const result = takeLastWhile(predicate, list)
  expect(result).toEqual([ 3, 4 ])
})

test('predicate is always true', () => {
  const predicate = () => true
  const result = takeLastWhile(predicate)(list)
  expect(result).toEqual(list)
})

test('predicate is always false', () => {
  const predicate = () => false
  const result = takeLastWhile(predicate, list)
  expect(result).toEqual([])
})

test('with string', () => {
  const result = takeLastWhile(x => x !== 'F', 'FOOBAR')
  expect(result).toBe('OOBAR')
})

takeUntil

takeUntil<T>(predicate: (x: T) => boolean, list: T[]): T[]

const list = [1, 2, 3, 4, 5]
const predicate = x => x > 3
const result = R.takeUntil(predicate, list)

// => [1, 2, 3]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%203%0Aconst%20result%20%3D%20R.takeUntil(predicate%2C%20list)%0A%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%203%5D">Try this <strong>R.takeUntil</strong> example in Rambda REPL</a>

export function takeUntil(predicate, list){
  const toReturn = []
  let stopFlag = false
  let counter = -1

  while (stopFlag === false && counter++ < list.length - 1){
    if (predicate(list[ counter ])){
      stopFlag = true
    } else {
      toReturn.push(list[ counter ])
    }
  }

  return toReturn
}

import { takeUntil } from './takeUntil.js'

const list = [ 1, 2, 3, 4, 5, 6 ]

test('happy', () => {
  const result = takeUntil(x => x > 3, list)
  expect(result).toEqual([ 1, 2, 3 ])
})

test('predicate always returns true', () => {
  const result = takeUntil(x => x < 10, list)
  expect(result).toEqual([])
})

test('predicate always returns false', () => {
  const result = takeUntil(x => x > 10, list)
  expect(result).toEqual(list)
})

takeWhile

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3C%203%0A%0Aconst%20result%20%3D%20R.takeWhile(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.takeWhile</strong> example in Rambda REPL</a>

tap

tap<T>(fn: (x: T) => void, input: T): T

It applies function fn to input x and returns x.

One use case is debugging in the middle of R.compose.

const list = [1, 2, 3]

R.compose(
  R.map(x => x * 2)
  R.tap(console.log),
  R.filter(x => x > 1)
)(list)
// => `2` and `3` will be logged

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0A%0AR.compose(%0A%20%20R.map(x%20%3D%3E%20x%20*%202)%0A%20%20R.tap(console.log)%2C%0A%20%20R.filter(x%20%3D%3E%20x%20%3E%201)%0A)(list)%0A%2F%2F%20%3D%3E%20%602%60%20and%20%603%60%20will%20be%20logged">Try this <strong>R.tap</strong> example in Rambda REPL</a>

export function tap(fn, x){
  if (arguments.length === 1) return _x => tap(fn, _x)

  fn(x)

  return x
}

import { tap } from './tap.js'

test('tap', () => {
  let a = 1
  const sayX = x => a = x

  expect(tap(sayX, 100)).toBe(100)
  expect(tap(sayX)(100)).toBe(100)
  expect(a).toBe(100)
})

tapAsync

tapAsync<T>(fn: Func<any> | Promise<any>, input: T): T

Asynchronous version of R.tap.

async function tapAsyncFn(fn, input){
  await fn(input)

  return input
}

export function tapAsync(fn, input){
  if (arguments.length === 1){
    return async _input => tapAsyncFn(fn, _input)
  }

  return new Promise((resolve, reject) => {
    tapAsyncFn(fn, input).then(resolve)
      .catch(reject)
  })
}

import { delay } from './delay.js'
import { pipedAsync } from './pipedAsync.js'
import { tapAsync } from './tapAsync.js'

test('happy', async () => {
  const result = await tapAsync(delay, 1)
  expect(result).toBe(1)
})

test('complex', async () => {
  let marker = false
  const fn = () => marker = true
  const result = await pipedAsync(
    1,
    async x => {
      await delay(100)

      return x + 1
    },
    tapAsync(fn),
    x => x + 1
  )
  expect(marker).toBeTrue()
  expect(result).toBe(3)
})

test

test(regExpression: RegExp): (str: string) => boolean

It determines whether str matches regExpression.

R.test(/^f/, 'foo')
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.test(%2F%5Ef%2F%2C%20'foo')%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.test</strong> example in Rambda REPL</a>

export function test(pattern, str){
  if (arguments.length === 1) return _str => test(pattern, _str)

  if (typeof pattern === 'string'){
    throw new TypeError(`R.test requires a value of type RegExp as its first argument; received "${ pattern }"`)
  }

  return str.search(pattern) !== -1
}

import { test as testMethod } from './test.js'

test('happy', () => {
  expect(testMethod(/^x/, 'xyz')).toBeTrue()

  expect(testMethod(/^y/)('xyz')).toBeFalse()
})

test('throws if first argument is not regex', () => {
  expect(() => testMethod('foo', 'bar')).toThrowErrorMatchingInlineSnapshot('"R.test requires a value of type RegExp as its first argument; received "foo""')
})

throttle

throttle<T>(fn: () => T, ms: number): () => T

let counter = 0
const inc = () => {
  counter++
}

const throttledInc = R.throttle(inc, 800)

const result = async () => {
  throttledInc()
  await R.delay(500)
  throttledInc()

  return counter
}
// `result` resolves to `1`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?let%20counter%20%3D%200%0Aconst%20inc%20%3D%20()%20%3D%3E%20%7B%0A%20%20counter%2B%2B%0A%7D%0A%0Aconst%20throttledInc%20%3D%20R.throttle(inc%2C%20800)%0A%0Aconst%20result%20%3D%20async%20()%20%3D%3E%20%7B%0A%20%20throttledInc()%0A%20%20await%20R.delay(500)%0A%20%20throttledInc()%0A%0A%20%20return%20counter%0A%7D%0A%2F%2F%20%60result%60%20resolves%20to%20%601%60">Try this <strong>R.throttle</strong> example in Rambda REPL</a>

export function throttle(fn, ms){
  let wait = false
  let result

  return function (...input){
    if (!wait){
      result = fn.apply(null, input)
      wait = true
      setTimeout(() => {
        wait = false
      }, ms)
    }

    return result
  }
}

import { delay } from './delay.js'
import { inc } from './inc.js'
import { throttle } from './throttle.js'

test('with side effect', async () => {
  let counter = 0

  const incFn = a => {
    counter += a

    return counter
  }
  const incWrapped = throttle(incFn, 1000)
  incWrapped(1)
  incWrapped(1)
  await delay(1500)
  incWrapped(1)
  expect(counter).toBe(2)
})

test('return result', async () => {
  const incWrapped = throttle(inc, 1000)
  const results = []
  results.push(incWrapped(1))
  results.push(incWrapped(1))
  await delay(1500)
  results.push(incWrapped(1))
  await delay(500)
  results.push(incWrapped(1))
  expect(results).toEqual([ 2, 2, 2, 2 ])
})

times

times<T>(fn: (i: number) => T, howMany: number): T[]

It returns the result of applying function fn over members of range array.

The range array includes numbers between 0 and howMany(exclusive).

const fn = x => x * 2
const howMany = 5

R.times(fn, howMany)
// => [0, 2, 4, 6, 8]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20x%20%3D%3E%20x%20*%202%0Aconst%20howMany%20%3D%205%0A%0Aconst%20result%20%3D%20R.times(fn%2C%20howMany)%0A%2F%2F%20%3D%3E%20%5B0%2C%202%2C%204%2C%206%2C%208%5D">Try this <strong>R.times</strong> example in Rambda REPL</a>

import { isInteger } from './_internals/isInteger.js'
import { map } from './map.js'
import { range } from './range.js'

export function times(fn, howMany){
  if (arguments.length === 1) return _howMany => times(fn, _howMany)
  if (!isInteger(howMany) || howMany < 0){
    throw new RangeError('n must be an integer')
  }

  return map(fn, range(0, howMany))
}

import assert from 'assert'

import { identity } from './identity.js'
import { times } from './times.js'

test('happy', () => {
  const result = times(identity, 5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

test('with bad input', () => {
  assert.throws(() => {
    times(3)('cheers!')
  }, RangeError)
  assert.throws(() => {
    times(identity, -1)
  }, RangeError)
})

test('curry', () => {
  const result = times(identity)(5)

  expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})

toDecimal

toDecimal(num: number, charsAfterDecimalPoint?: number): number

R.toDecimal(2.45464,2) // => 2.45

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.toDecimal(2.45464%2C2)%20%2F%2F%20%3D%3E%202.45">Try this <strong>R.toDecimal</strong> example in Rambda REPL</a>

export function toDecimal(number, charsAfterDecimalPoint = 2){
  return Number(parseFloat(String(number)).toFixed(charsAfterDecimalPoint))
}

import { toDecimal } from './toDecimal.js'

test('happy', () => {
  expect(toDecimal(2.2789, 1)).toBe(2.3)
  expect(toDecimal(2.2789, 3)).toBe(2.279)
  expect(toDecimal(2, 3)).toBe(2)
  expect(toDecimal(2.2789)).toBe(2.28)
  expect(toDecimal(2.45464)).toBe(2.45)
})

toLower

toLower<S extends string>(str: S): Lowercase<S>

R.toLower('FOO')
// => 'foo'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.toLower('FOO')%0A%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.toLower</strong> example in Rambda REPL</a>

export function toLower(str){
  return str.toLowerCase()
}

import { toLower } from './toLower.js'

test('toLower', () => {
  expect(toLower('FOO|BAR|BAZ')).toBe('foo|bar|baz')
})

toPairs

toPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>

It transforms an object to a list.

const list = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]

const result = R.toPairs(list)
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%202%2C%0A%20%20c%20%3A%20%5B%203%2C%204%20%5D%2C%0A%7D%0Aconst%20expected%20%3D%20%5B%20%5B%20'a'%2C%201%20%5D%2C%20%5B%20'b'%2C%202%20%5D%2C%20%5B%20'c'%2C%20%5B%203%2C%204%20%5D%20%5D%20%5D%0A%0Aconst%20result%20%3D%20R.toPairs(list)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.toPairs</strong> example in Rambda REPL</a>

export function toPairs(obj){
  return Object.entries(obj)
}

import { toPairs } from './toPairs.js'

const obj = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [
  [ 'a', 1 ],
  [ 'b', 2 ],
  [ 'c', [ 3, 4 ] ],
]

test('happy', () => {
  expect(toPairs(obj)).toEqual(expected)
})

toString

toString(x: unknown): string

R.toString([1, 2]) 
// => '1,2'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.toString(%5B1%2C%202%5D)%20%0A%2F%2F%20%3D%3E%20'1%2C2'">Try this <strong>R.toString</strong> example in Rambda REPL</a>

export function toString(x){
  return x.toString()
}

import { toString } from './toString.js'

test('happy', () => {
  expect(toString([ 1, 2, 3 ])).toBe('1,2,3')
})

toUpper

toUpper<S extends string>(str: S): Uppercase<S>

R.toUpper('foo')
// => 'FOO'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.toUpper('foo')%0A%2F%2F%20%3D%3E%20'FOO'">Try this <strong>R.toUpper</strong> example in Rambda REPL</a>

export function toUpper(str){
  return str.toUpperCase()
}

import { toUpper } from './toUpper.js'

test('toUpper', () => {
  expect(toUpper('foo|bar|baz')).toBe('FOO|BAR|BAZ')
})

transpose

transpose<T>(list: (T[])[]): (T[])[]

const list = [[10, 11], [20], [], [30, 31, 32]]
const expected = [[10, 20, 30], [11, 31], [32]]

const result = R.transpose(list)
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%5B10%2C%2011%5D%2C%20%5B20%5D%2C%20%5B%5D%2C%20%5B30%2C%2031%2C%2032%5D%5D%0Aconst%20expected%20%3D%20%5B%5B10%2C%2020%2C%2030%5D%2C%20%5B11%2C%2031%5D%2C%20%5B32%5D%5D%0A%0Aconst%20result%20%3D%20R.transpose(list)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.transpose</strong> example in Rambda REPL</a>

import { isArray } from './_internals/isArray.js'

export function transpose(array){
  return array.reduce((acc, el) => {
    el.forEach((nestedEl, i) =>
      isArray(acc[ i ]) ? acc[ i ].push(nestedEl) : acc.push([ nestedEl ]))

    return acc
  }, [])
}

import { transpose } from './transpose.js'

test('happy', () => {
  const input = [
    [ 'a', 1 ],
    [ 'b', 2 ],
    [ 'c', 3 ],
  ]

  expect(transpose(input)).toEqual([
    [ 'a', 'b', 'c' ],
    [ 1, 2, 3 ],
  ])
})

test('when rows are shorter', () => {
  const actual = transpose([ [ 10, 11 ], [ 20 ], [], [ 30, 31, 32 ] ])
  const expected = [ [ 10, 20, 30 ], [ 11, 31 ], [ 32 ] ]
  expect(actual).toEqual(expected)
})

test('with empty array', () => {
  expect(transpose([])).toEqual([])
})

test('array with falsy values', () => {
  const actual = transpose([
    [ true, false, undefined, null ],
    [ null, undefined, false, true ],
  ])
  const expected = [
    [ true, null ],
    [ false, undefined ],
    [ undefined, false ],
    [ null, true ],
  ]
  expect(actual).toEqual(expected)
})

trim

trim(str: string): string

R.trim('  foo  ') 
// => 'foo'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.trim('%20%20foo%20%20')%20%0A%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.trim</strong> example in Rambda REPL</a>

export function trim(str){
  return str.trim()
}

import { trim } from './trim.js'

test('trim', () => {
  expect(trim(' foo ')).toBe('foo')
})

tryCatch

It returns function that runs fn in try/catch block. If there was an error, then fallback is used to return the result. Note that fn can be value or asynchronous/synchronous function(unlike Ramda where fallback can only be a synchronous function).

:boom: Please check the tests of R.tryCatch to fully understand how this method works.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20x%20%3D%3E%20x.foo%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.tryCatch(fn%2C%20false)(null)%2C%0A%20%20R.tryCatch(fn%2C%20false)(%7Bfoo%3A%20'bar'%7D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20'bar'%5D">Try this <strong>R.tryCatch</strong> example in Rambda REPL</a>

tryCatchAsync

It returns function that runs fn in try/catch block. If there was an error, then fallback is used to return the result.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%20%7Bfoo%3A%201%7D%0Aconst%20fnFoo%20%3D%20async%20()%20%3D%3E%20x.foo%0Aconst%20fnBar%20%3D%20async%20()%20%3D%3E%20x.bar%0A%0Aconst%20result%20%3D%20await%20Promise.all(%5B%0A%20%20R.tryCatchAsync%20(fnFoo%2C%20false)()%2C%0A%20%20R.tryCatchAsync(fnBar%2C%20false)()%0A%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%20false%5D">Try this <strong>R.tryCatchAsync</strong> example in Rambda REPL</a>

type

It accepts any input and it returns its type.

:boom: NaN, Promise and Async are types specific for Rambda.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.type(()%20%3D%3E%20%7B%7D)%20%2F%2F%20%3D%3E%20'Function'%0AR.type(async%20()%20%3D%3E%20%7B%7D)%20%2F%2F%20%3D%3E%20'Async'%0AR.type(%5B%5D)%20%2F%2F%20%3D%3E%20'Array'%0AR.type(%7B%7D)%20%2F%2F%20%3D%3E%20'Object'%0AR.type('foo')%20%2F%2F%20%3D%3E%20'String'%0AR.type(1)%20%2F%2F%20%3D%3E%20'Number'%0AR.type(true)%20%2F%2F%20%3D%3E%20'Boolean'%0AR.type(null)%20%2F%2F%20%3D%3E%20'Null'%0AR.type(%2F%5BA-z%5D%2F)%20%2F%2F%20%3D%3E%20'RegExp'%0AR.type('foo'*1)%20%2F%2F%20%3D%3E%20'NaN'%0A%0Aconst%20delay%20%3D%20ms%20%3D%3E%20new%20Promise(resolve%20%3D%3E%20%7B%0A%20%20setTimeout(function%20()%20%7B%0A%20%20%20%20resolve()%0A%20%20%7D%2C%20ms)%0A%7D)%0AR.type(delay)%20%2F%2F%20%3D%3E%20'Promise'">Try this <strong>R.type</strong> example in Rambda REPL</a>

unapply

unapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T

It calls a function fn with the list of values of the returned function.

R.unapply is the opposite of R.apply method.

R.unapply(JSON.stringify)(1, 2, 3)
//=> '[1,2,3]'

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.unapply(JSON.stringify)(1%2C%202%2C%203)%0A%2F%2F%3D%3E%20'%5B1%2C2%2C3%5D'">Try this <strong>R.unapply</strong> example in Rambda REPL</a>

export function unapply(fn){
  return function (...args){
    return fn.call(this, args)
  }
}

import { apply } from './apply.js'
import { converge } from './converge.js'
import { identity } from './identity.js'
import { prop } from './prop.js'
import { sum } from './sum.js'
import { unapply } from './unapply.js'

test('happy', () => {
  const fn = unapply(identity)
  expect(fn(
    1, 2, 3
  )).toEqual([ 1, 2, 3 ])
  expect(fn()).toEqual([])
})

test('returns a function which is always passed one argument', () => {
  const fn = unapply(function (){
    return arguments.length
  })
  expect(fn('x')).toBe(1)
  expect(fn('x', 'y')).toBe(1)
  expect(fn(
    'x', 'y', 'z'
  )).toBe(1)
})

test('forwards arguments to decorated function as an array', () => {
  const fn = unapply(xs => '[' + xs + ']')
  expect(fn(2)).toBe('[2]')
  expect(fn(2, 4)).toBe('[2,4]')
  expect(fn(
    2, 4, 6
  )).toBe('[2,4,6]')
})

test('returns a function with length 0', () => {
  const fn = unapply(identity)
  expect(fn).toHaveLength(0)
})

test('is the inverse of R.apply', () => {
  let a, b, c, d, e, f, g, n
  const rand = function (){
    return Math.floor(200 * Math.random()) - 100
  }

  f = Math.max
  g = unapply(apply(f))
  n = 1
  while (n <= 100){
    a = rand()
    b = rand()
    c = rand()
    d = rand()
    e = rand()
    expect(f(
      a, b, c, d, e
    )).toEqual(g(
      a, b, c, d, e
    ))
    n += 1
  }

  f = function (xs){
    return '[' + xs + ']'
  }
  g = apply(unapply(f))
  n = 1
  while (n <= 100){
    a = rand()
    b = rand()
    c = rand()
    d = rand()
    e = rand()
    expect(f([ a, b, c, d, e ])).toEqual(g([ a, b, c, d, e ]))
    n += 1
  }
})

test('it works with converge', () => {
  const fn = unapply(sum)
  const convergeFn = converge(fn, [ prop('a'), prop('b'), prop('c') ])
  const obj = {
    a : 1337,
    b : 42,
    c : 1,
  }
  const expected = 1337 + 42 + 1
  expect(convergeFn(obj)).toEqual(expected)
})

union

union<T>(x: T[], y: T[]): T[]

It takes two lists and return a new list containing a merger of both list with removed duplicates.

R.equals is used to compare for duplication.

const result = R.union([1,2,3], [3,4,5]);
// => [1, 2, 3, 4, 5]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.union(%5B1%2C2%2C3%5D%2C%20%5B3%2C4%2C5%5D)%3B%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%203%2C%204%2C%205%5D">Try this <strong>R.union</strong> example in Rambda REPL</a>

import { cloneList } from './_internals/cloneList.js'
import { includes } from './includes.js'

export function union(x, y){
  if (arguments.length === 1) return _y => union(x, _y)

  const toReturn = cloneList(x)

  y.forEach(yInstance => {
    if (!includes(yInstance, x)) toReturn.push(yInstance)
  })

  return toReturn
}

import { union } from './union.js'

test('happy', () => {
  expect(union([ 1, 2 ], [ 2, 3 ])).toEqual([ 1, 2, 3 ])
})

test('with list of objects', () => {
  const list1 = [ { a : 1 }, { a : 2 } ]
  const list2 = [ { a : 2 }, { a : 3 } ]
  const result = union(list1)(list2)
})

uniq

uniq<T>(list: T[]): T[]

It returns a new array containing only one copy of each element of list.

R.equals is used to determine equality.

const list = [1, 1, {a: 1}, {a: 2}, {a:1}]

R.uniq(list)
// => [1, {a: 1}, {a: 2}]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%201%2C%20%7Ba%3A%201%7D%2C%20%7Ba%3A%202%7D%2C%20%7Ba%3A1%7D%5D%0A%0Aconst%20result%20%3D%20R.uniq(list)%0A%2F%2F%20%3D%3E%20%5B1%2C%20%7Ba%3A%201%7D%2C%20%7Ba%3A%202%7D%5D">Try this <strong>R.uniq</strong> example in Rambda REPL</a>

import { _Set } from './_internals/set.js'

export function uniq(list){
  const set = new _Set()
  const willReturn = []
  list.forEach(item => {
    if (set.checkUniqueness(item)){
      willReturn.push(item)
    }
  })

  return willReturn
}

import { uniq } from './uniq.js'

test('happy', () => {
  const list = [ 1, 2, 3, 3, 3, 1, 2, 0 ]
  expect(uniq(list)).toEqual([ 1, 2, 3, 0 ])
})

test('with object', () => {
  const list = [ { a : 1 }, { a : 2 }, { a : 1 }, { a : 2 } ]
  expect(uniq(list)).toEqual([ { a : 1 }, { a : 2 } ])
})

test('with nested array', () => {
  expect(uniq([ [ 42 ], [ 42 ] ])).toEqual([ [ 42 ] ])
})

test('with booleans', () => {
  expect(uniq([ [ false ], [ false ], [ true ] ])).toEqual([ [ false ], [ true ] ])
})

test('with falsy values', () => {
  expect(uniq([ undefined, null ])).toEqual([ undefined, null ])
})

test('can distinct between string and number', () => {
  expect(uniq([ 1, '1' ])).toEqual([ 1, '1' ])
})

uniqBy

It applies uniqueness to input list based on function that defines what to be used for comparison between elements.

R.equals is used to determine equality.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%2C%20%7Ba%3A1%7D%5D%0Aconst%20result%20%3D%20R.uniqBy(x%20%3D%3E%20x%2C%20list)%0A%0A%2F%2F%20%3D%3E%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%5D">Try this <strong>R.uniqBy</strong> example in Rambda REPL</a>

uniqWith

uniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[]

It returns a new array containing only one copy of each element in list according to predicate function.

This predicate should return true, if two elements are equal.

const list = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
  {id: 3, title:'foo'},
  {id: 4, title:'bar'},
]

const expected = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
]

const predicate = (x,y) => x.title === y.title

const result = R.uniqWith(predicate, list)
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Bid%3A%200%2C%20title%3A'foo'%7D%2C%0A%20%20%7Bid%3A%201%2C%20title%3A'bar'%7D%2C%0A%20%20%7Bid%3A%202%2C%20title%3A'baz'%7D%2C%0A%20%20%7Bid%3A%203%2C%20title%3A'foo'%7D%2C%0A%20%20%7Bid%3A%204%2C%20title%3A'bar'%7D%2C%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Bid%3A%200%2C%20title%3A'foo'%7D%2C%0A%20%20%7Bid%3A%201%2C%20title%3A'bar'%7D%2C%0A%20%20%7Bid%3A%202%2C%20title%3A'baz'%7D%2C%0A%5D%0A%0Aconst%20predicate%20%3D%20(x%2Cy)%20%3D%3E%20x.title%20%3D%3D%3D%20y.title%0A%0Aconst%20result%20%3D%20R.uniqWith(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.uniqWith</strong> example in Rambda REPL</a>

function includesWith(
  predicate, target, list
){
  let willReturn = false
  let index = -1

  while (++index < list.length && !willReturn){
    const value = list[ index ]

    if (predicate(target, value)){
      willReturn = true
    }
  }

  return willReturn
}

export function uniqWith(predicate, list){
  if (arguments.length === 1) return _list => uniqWith(predicate, _list)

  let index = -1
  const willReturn = []

  while (++index < list.length){
    const value = list[ index ]

    if (!includesWith(
      predicate, value, willReturn
    )){
      willReturn.push(value)
    }
  }

  return willReturn
}

import { uniqWith as uniqWithRamda } from 'ramda'

import { uniqWith } from './uniqWith.js'

const list = [ { a : 1 }, { a : 1 } ]

test('happy', () => {
  const fn = (x, y) => x.a === y.a

  const result = uniqWith(fn, list)
  expect(result).toEqual([ { a : 1 } ])
})

test('with list of strings', () => {
  const fn = (x, y) => x.length === y.length
  const list = [ '0', '11', '222', '33', '4', '55' ]
  const result = uniqWith(fn)(list)
  const resultRamda = uniqWithRamda(fn, list)
  expect(result).toEqual([ '0', '11', '222' ])
  expect(resultRamda).toEqual([ '0', '11', '222' ])
})

unless

unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U

The method returns function that will be called with argument input.

If predicate(input) returns false, then the end result will be the outcome of whenFalse(input).

In the other case, the final output will be the input itself.

const fn = R.unless(
  x => x > 2,
  x => x + 10
)

const result = [
  fn(1),
  fn(5)
]
// => [11, 5]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.unless(%0A%20%20x%20%3D%3E%20x%20%3E%202%2C%0A%20%20x%20%3D%3E%20x%20%2B%2010%0A)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20fn(1)%2C%0A%20%20fn(5)%0A%5D%0A%2F%2F%20%3D%3E%20%5B11%2C%205%5D">Try this <strong>R.unless</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

function unlessFn(
  predicate, whenFalseFn, input
){
  if (predicate(input)) return input

  return whenFalseFn(input)
}

export const unless = curry(unlessFn)

import { inc } from './inc.js'
import { isNil } from './isNil.js'
import { unless } from './unless.js'

test('happy', () => {
  const safeInc = unless(isNil, inc)
  expect(safeInc(null)).toBeNull()
  expect(safeInc(1)).toBe(2)
})

test('curried', () => {
  const safeIncCurried = unless(isNil)(inc)
  expect(safeIncCurried(null)).toBeNull()
})

test('with 3 inputs', () => {
  let result = unless(x => x.startsWith('/'), x=> x.concat('/'), '/api')
  expect(result).toBe('/api')
})

unnest

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.unnest(%5B1%2C%20%5B2%5D%2C%20%5B%5B3%5D%5D%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%20%5B3%5D%5D">Try this <strong>R.unnest</strong> example in Rambda REPL</a>

unwind

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%3A%201%2C%0A%20%20b%3A%20%5B2%2C%203%5D%2C%0A%7D%0Aconst%20result%20%3D%20R.unwind('b'%2C%20obj)%0Aconst%20expected%20%3D%20%5B%7Ba%3A1%2C%20b%3A2%7D%2C%20%7Ba%3A1%2C%20b%3A3%7D%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.unwind</strong> example in Rambda REPL</a>

update

update<T>(index: number, newValue: T, list: T[]): T[]

It returns a copy of list with updated element at index with newValue.

const index = 2
const newValue = 88
const list = [1, 2, 3, 4, 5]

const result = R.update(index, newValue, list)
// => [1, 2, 88, 4, 5]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20index%20%3D%202%0Aconst%20newValue%20%3D%2088%0Aconst%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0A%0Aconst%20result%20%3D%20R.update(index%2C%20newValue%2C%20list)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%2088%2C%204%2C%205%5D">Try this <strong>R.update</strong> example in Rambda REPL</a>

import { cloneList } from './_internals/cloneList.js'
import { curry } from './curry.js'

export function updateFn(
  index, newValue, list
){
  const clone = cloneList(list)
  if (index === -1) return clone.fill(newValue, index)

  return clone.fill(
    newValue, index, index + 1
  )
}

export const update = curry(updateFn)

import { update } from './update.js'

const list = [ 1, 2, 3 ]

test('happy', () => {
  const newValue = 8
  const index = 1
  const result = update(
    index, newValue, list
  )
  const curriedResult = update(index, newValue)(list)
  const tripleCurriedResult = update(index)(newValue)(list)

  const expected = [ 1, 8, 3 ]
  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
  expect(tripleCurriedResult).toEqual(expected)
})

test('list has no such index', () => {
  const newValue = 8
  const index = 10
  const result = update(
    index, newValue, list
  )

  expect(result).toEqual(list)
})

test('with negative index', () => {
  expect(update(
    -1, 10, [ 1 ]
  )).toEqual([ 10 ])
  expect(update(
    -1, 10, []
  )).toEqual([])
  expect(update(
    -1, 10, list
  )).toEqual([ 1, 2, 10 ])
  expect(update(
    -2, 10, list
  )).toEqual([ 1, 10, 3 ])
  expect(update(
    -3, 10, list
  )).toEqual([ 10, 2, 3 ])
})

updateObject

updateObject<Output>(rules: ([string, any])[], input: object): Output

Very similar to R.assocPath but it applies list of updates instead of only a single update.

It returns a copy of obj input with changed properties according to rules input.

Each instance of rules is a tuple of object path and the new value for this path. If such object path does not exist, then such object path is created.

As it uses R.path underneath, object path can be either string or array of strings(in Typescript object path can be only a string).

const obj = {
  a: {b: 1},
  foo: {bar: 10},
}
const rules = [
  ['a.b', 2],
  ['foo.bar', 20],
  ['q.z', 300],
]
const result = R.updateObject(rules, Record<string, unknown>)

const expected = {
  a: {b: 2},
  foo: {bar: 20},
  q: {z: 300},
}
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%3A%20%7Bb%3A%201%7D%2C%0A%20%20foo%3A%20%7Bbar%3A%2010%7D%2C%0A%7D%0Aconst%20rules%20%3D%20%5B%0A%20%20%5B'a.b'%2C%202%5D%2C%0A%20%20%5B'foo.bar'%2C%2020%5D%2C%0A%20%20%5B'q.z'%2C%20300%5D%2C%0A%5D%0Aconst%20result%20%3D%20R.updateObject(rules%2C%20Record%3Cstring%2C%20unknown%3E)%0A%0Aconst%20expected%20%3D%20%7B%0A%20%20a%3A%20%7Bb%3A%202%7D%2C%0A%20%20foo%3A%20%7Bbar%3A%2020%7D%2C%0A%20%20q%3A%20%7Bz%3A%20300%7D%2C%0A%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.updateObject</strong> example in Rambda REPL</a>

import { assocPath } from './assocPath.js'

export function updateObject(rules, obj){
  if (arguments.length === 1) return _obj => updateObject(rules, _obj)

  let clone = { ...obj } /*?.*/

  rules.forEach(([ objectPath, newValue ]) => {
    clone = assocPath(
      objectPath, newValue, clone
    )
  })

  return clone
}

import { updateObject } from './updateObject.js'

const obj = {
  a   : { b : 1 },
  foo : { bar : 10 },
}
const rules = [
  [ 'a.b', 2 ],
  [ 'foo.bar', 20 ],
  [ 'q.z', 300 ],
]
const expected = {
  a   : { b : 2 },
  foo : { bar : 20 },
  q   : { z : 300 },
}

test('happy', () => {
  const result = updateObject(rules, obj)
  expect(result).toEqual(expected)
})

test('curried', () => {
  const result = updateObject(rules)(obj)
  expect(result).toEqual(expected)
})

values

values<T extends object, K extends keyof T>(obj: T): T[K][]

With correct input, this is nothing more than Object.values(Record<string, unknown>). If obj is not an object, then it returns an empty array.

const obj = {a:1, b:2}

R.values(Record<string, unknown>)
// => [1, 2]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A1%2C%20b%3A2%7D%0A%0Aconst%20result%20%3D%20R.values(Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.values</strong> example in Rambda REPL</a>

import { type } from './type.js'

export function values(obj){
  if (type(obj) !== 'Object') return []
  return Object.values(obj)
}

import { values } from './values.js'

test('happy', () => {
  expect(values({
    a : 1,
    b : 2,
    c : 3,
  })).toEqual([ 1, 2, 3 ])
})

test('with bad input', () => {
  expect(values(null)).toEqual([])
  expect(values(undefined)).toEqual([])
  expect(values(55)).toEqual([])
  expect(values('foo')).toEqual([])
  expect(values(true)).toEqual([])
  expect(values(false)).toEqual([])
  expect(values(NaN)).toEqual([])
  expect(values(Infinity)).toEqual([])
  expect(values([])).toEqual([])
})

view

view<S, A>(lens: Lens<S, A>): (obj: S) => A

It returns the value of lens focus over target object.

const lens = R.lensProp('x')

R.view(lens, {x: 1, y: 2}) // => 1
R.view(lens, {x: 4, y: 2}) // => 4

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20lens%20%3D%20R.lensProp('x')%0A%0AR.view(lens%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%201%0Aconst%20result%20%3D%20R.view(lens%2C%20%7Bx%3A%204%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%204">Try this <strong>R.view</strong> example in Rambda REPL</a>

const Const = x => ({
  x,
  map : fn => Const(x),
})

export function view(lens, target){
  if (arguments.length === 1) return _target => view(lens, _target)

  return lens(Const)(target).x
}

import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { prop } from './prop.js'
import { view } from './view.js'

const testObject = { foo : 'Led Zeppelin' }
const assocLens = lens(prop('foo'), assoc('foo'))

test('happy', () => {
  expect(view(assocLens, testObject)).toBe('Led Zeppelin')
})

viewOr

viewOr<Input, Output>(fallback: Output, lens: Lens<Input, Output>, input: Input): Output

A combination between R.defaultTo and `R.view.

const lens = R.lensProp('a');
const input = {a: 'foo'}
const fallbackInput = {b: 'bar'}
const fallback = 'FALLBACK'

const result = [
  R.viewOr(fallback, lens, input),
  R.viewOr(fallback, lens, fallbackInput)
]
// => ['foo', 'FALLBACK']

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20lens%20%3D%20R.lensProp('a')%3B%0Aconst%20input%20%3D%20%7Ba%3A%20'foo'%7D%0Aconst%20fallbackInput%20%3D%20%7Bb%3A%20'bar'%7D%0Aconst%20fallback%20%3D%20'FALLBACK'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.viewOr(fallback%2C%20lens%2C%20input)%2C%0A%20%20R.viewOr(fallback%2C%20lens%2C%20fallbackInput)%0A%5D%0A%2F%2F%20%3D%3E%20%5B'foo'%2C%20'FALLBACK'%5D">Try this <strong>R.viewOr</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { defaultTo } from './defaultTo.js'
import { view } from './view.js'

function viewOrFn(
  fallback, lens, input
){
  return defaultTo(fallback, view(lens, input))
}

export const viewOr = curry(viewOrFn)

import { lensProp } from './lensProp.js'
import { viewOr } from './viewOr.js'

const lens = lensProp('a')
const input = { a : 'foo' }
const fallbackInput = { b : 'bar' }
const fallback = 'FALLBACK'

test('happy', () => {
  const result = viewOr(
    fallback, lens, fallbackInput
  )
  expect(result).toBe(fallback)
})

test('curried', () => {
  const result = viewOr(fallback, lens)(input)
  expect(result).toBe('foo')
})

wait

wait<T>(fn: Promise<T>): Promise<[T, Error|undefined]>

It provides Golang-like interface for handling promises.

const [result, err] = await R.wait(R.delay(1000))
// => err is undefined
// => result is `RAMBDAX_DELAY`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20const%20%5Bresult%2C%20err%5D%20%3D%20await%20R.wait(R.delay(1000))%0A%2F%2F%20%3D%3E%20err%20is%20undefined%0A%2F%2F%20%3D%3E%20result%20is%20%60RAMBDAX_DELAY%60">Try this <strong>R.wait</strong> example in Rambda REPL</a>

export function wait(fn){
  return new Promise(resolve => {
    fn.then(result => resolve([ result, undefined ])).catch(e =>
      resolve([ undefined, e ]))
  })
}

import { wait } from './wait.js'

test('happy path', async () => {
  const fn = x => Promise.resolve(x + 1)
  const [ result, err ] = await wait(fn(1))

  expect(result).toBe(2)
  expect(err).toBeUndefined()
})

test('when promise is rejected', async () => {
  const fn = x => Promise.reject(Error('foo'))
  const [ result, err ] = await wait(fn(1))

  expect(result).toBeUndefined()
  expect(err).toEqual(Error('foo'))
})

waitFor

waitFor(
  waitForTrueCondition: () => boolean,
  howLong: number,
  loops?: number
): () => Promise<boolean>

It returns true, if condition returns true within howLong milliseconds time period.

The method accepts an optional third argument loops(default to 10), which is the number of times waitForTrueCondition will be evaluated for howLong period. Once this function returns a value different from false, this value will be the final result.

Otherwise, R.waitFor will return false.

const howLong = 1000
let counter = 0
const waitForTrueCondition = async x => {
  await R.delay(100)
  counter = counter + x

  return counter > 10
}

const result = await R.waitFor(waitForTrueCondition, howLong)(2)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20howLong%20%3D%201000%0Alet%20counter%20%3D%200%0Aconst%20waitForTrueCondition%20%3D%20async%20x%20%3D%3E%20%7B%0A%20%20await%20R.delay(100)%0A%20%20counter%20%3D%20counter%20%2B%20x%0A%0A%20%20return%20counter%20%3E%2010%0A%7D%0A%0Aconst%20result%20%3D%20await%20R.waitFor(waitForTrueCondition%2C%20howLong)(2)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.waitFor</strong> example in Rambda REPL</a>

import { delay } from './delay.js'
import { range } from './range.js'
import { type } from './type.js'

export function waitFor(
  condition, howLong, loops = 10
){
  const typeCondition = type(condition)

  const passPromise = typeCondition === 'Promise'
  const passFunction = typeCondition === 'Function'
  const interval = Math.floor(howLong / loops)

  if (!(passPromise || passFunction)){
    throw new Error('R.waitFor')
  }

  return async (...inputs) => {
    for (const _ of range(0, loops)){
      const resultCondition = await condition(...inputs)

      if (resultCondition === false){
        await delay(interval)
      } else {
        return resultCondition
      }
    }

    return false
  }
}

import { delay } from './delay.js'
import { waitFor } from './waitFor.js'

const howLong = 1000

test('true', async () => {
  let counter = 0
  const condition = x => {
    counter++

    return counter > x
  }

  const result = await waitFor(condition, howLong)(6)
  expect(result).toBeTrue()
})

test('false', async () => {
  let counter = 0
  const condition = x => {
    counter++

    return counter > x
  }

  const result = await waitFor(condition, howLong)(12)
  expect(result).toBeFalse()
})

test('async condition | true', async () => {
  let counter = 0
  const condition = async x => {
    counter++
    await delay(10)

    return counter > x
  }

  const result = await waitFor(condition, howLong)(6)
  expect(result).toBeTrue()
})

test('async condition | false', async () => {
  let counter = 0
  const condition = async x => {
    counter++
    await delay(10)

    return counter > x
  }

  const result = await waitFor(condition, howLong)(12)
  expect(result).toBeFalse()
})

test('throws when fn is not function', () => {
  const fn = 'foo'

  expect(() => waitFor(fn, howLong)()).toThrowErrorMatchingInlineSnapshot('"R.waitFor"')
})

when

when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U

It pass input to predicate function and if the result is true, it will return the result of whenTrueFn(input). If the predicate returns false, then it will simply return input.

const predicate = x => typeof x === 'number'
const whenTrueFn = R.add(11)

const fn = when(predicate, whenTrueResult)

const positiveInput = 88
const negativeInput = 'foo'

const result = [
  fn(positiveInput),
  fn(positiveInput),
]

const expected = [
  99,
  'foo',
]
// => `result` is equal to `expected`

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20typeof%20x%20%3D%3D%3D%20'number'%0Aconst%20whenTrueFn%20%3D%20R.add(11)%0A%0Aconst%20fn%20%3D%20when(predicate%2C%20whenTrueResult)%0A%0Aconst%20positiveInput%20%3D%2088%0Aconst%20negativeInput%20%3D%20'foo'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20fn(positiveInput)%2C%0A%20%20fn(positiveInput)%2C%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%2099%2C%0A%20%20'foo'%2C%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.when</strong> example in Rambda REPL</a>

import { curry } from './curry.js'

function whenFn(
  predicate, whenTrueFn, input
){
  if (!predicate(input)) return input

  return whenTrueFn(input)
}

export const when = curry(whenFn)

import { add } from './add.js'
import { when } from './when.js'

const predicate = x => typeof x === 'number'

test('happy', () => {
  const fn = when(predicate, add(11))
  expect(fn(11)).toBe(22)
  expect(fn('foo')).toBe('foo')
})

where

where<T, U>(conditions: T, input: U): boolean

It returns true if all each property in conditions returns true when applied to corresponding property in input object.

const condition = R.where({
  a : x => typeof x === "string",
  b : x => x === 4
})
const input = {
  a : "foo",
  b : 4,
  c : 11,
}

const result = condition(input) 
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20condition%20%3D%20R.where(%7B%0A%20%20a%20%3A%20x%20%3D%3E%20typeof%20x%20%3D%3D%3D%20%22string%22%2C%0A%20%20b%20%3A%20x%20%3D%3E%20x%20%3D%3D%3D%204%0A%7D)%0Aconst%20input%20%3D%20%7B%0A%20%20a%20%3A%20%22foo%22%2C%0A%20%20b%20%3A%204%2C%0A%20%20c%20%3A%2011%2C%0A%7D%0A%0Aconst%20result%20%3D%20condition(input)%20%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.where</strong> example in Rambda REPL</a>

export function where(conditions, input){
  if (input === undefined){
    return _input => where(conditions, _input)
  }
  let flag = true
  for (const prop in conditions){
    if (!flag) continue
    const result = conditions[ prop ](input[ prop ])
    if (flag && result === false){
      flag = false
    }
  }

  return flag
}

import { equals } from './equals.js'
import { where } from './where.js'

test('when true', () => {
  const result = where({
    a : equals('foo'),
    b : equals('bar'),
  },
  {
    a : 'foo',
    b : 'bar',
    x : 11,
    y : 19,
  })

  expect(result).toBeTrue()
})

test('when false | early exit', () => {
  let counter = 0
  const equalsFn = expected => input => {
    console.log(expected, 'expected')
    counter++

    return input === expected
  }
  const predicate = where({
    a : equalsFn('foo'),
    b : equalsFn('baz'),
  })
  expect(predicate({
    a : 'notfoo',
    b : 'notbar',
  })).toBeFalse()
  expect(counter).toBe(1)
})

whereAny

Same as R.where, but it will return true if at least one condition check returns true.

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20conditions%20%3D%20%7B%0A%20%20a%3A%20a%20%3D%3E%20a%20%3E%201%2C%0A%20%20b%3A%20b%20%3D%3E%20b%20%3E%202%2C%0A%7D%0Aconst%20result%20%3D%20%5B%0A%20%20R.whereAny(conditions%2C%20%7Bb%3A3%7D)%2C%0A%20%20R.whereAny(conditions%2C%20%7Bc%3A4%7D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.whereAny</strong> example in Rambda REPL</a>

whereEq

whereEq<T, U>(condition: T, input: U): boolean

It will return true if all of input object fully or partially include rule object.

R.equals is used to determine equality.

const condition = { a : { b : 1 } }
const input = {
  a : { b : 1 },
  c : 2
}

const result = whereEq(condition, input)
// => true

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20condition%20%3D%20%7B%20a%20%3A%20%7B%20b%20%3A%201%20%7D%20%7D%0Aconst%20input%20%3D%20%7B%0A%20%20a%20%3A%20%7B%20b%20%3A%201%20%7D%2C%0A%20%20c%20%3A%202%0A%7D%0A%0Aconst%20result%20%3D%20whereEq(condition%2C%20input)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.whereEq</strong> example in Rambda REPL</a>

import { equals } from './equals.js'
import { filter } from './filter.js'

export function whereEq(condition, input){
  if (arguments.length === 1){
    return _input => whereEq(condition, _input)
  }

  const result = filter((conditionValue, conditionProp) =>
    equals(conditionValue, input[ conditionProp ]),
  condition)

  return Object.keys(result).length === Object.keys(condition).length
}

import { whereEq } from './whereEq.js'

test('when true', () => {
  const condition = { a : 1 }
  const input = {
    a : 1,
    b : 2,
  }

  const result = whereEq(condition, input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const condition = { a : 1 }
  const input = { b : 2 }

  const result = whereEq(condition, input)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

test('with nested object', () => {
  const condition = { a : { b : 1 } }
  const input = {
    a : { b : 1 },
    c : 2,
  }

  const result = whereEq(condition)(input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('with wrong input', () => {
  const condition = { a : { b : 1 } }

  expect(() => whereEq(condition, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'a\')"')
})

without

without<T>(matchAgainst: T[], source: T[]): T[]

It will return a new array, based on all members of source list that are not part of matchAgainst list.

R.equals is used to determine equality.

const source = [1, 2, 3, 4]
const matchAgainst = [2, 3]

const result = R.without(matchAgainst, source)
// => [1, 4]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20source%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20matchAgainst%20%3D%20%5B2%2C%203%5D%0A%0Aconst%20result%20%3D%20R.without(matchAgainst%2C%20source)%0A%2F%2F%20%3D%3E%20%5B1%2C%204%5D">Try this <strong>R.without</strong> example in Rambda REPL</a>

import { _indexOf } from './equals.js'
import { reduce } from './reduce.js'

export function without(matchAgainst, source){
  if (source === undefined){
    return _source => without(matchAgainst, _source)
  }

  return reduce(
    (prev, current) =>
      _indexOf(current, matchAgainst) > -1 ? prev : prev.concat(current),
    [],
    source
  )
}

import { without as withoutRamda } from 'ramda'

import { without } from './without.js'

test('should return a new list without values in the first argument', () => {
  const itemsToOmit = [ 'A', 'B', 'C' ]
  const collection = [ 'A', 'B', 'C', 'D', 'E', 'F' ]

  expect(without(itemsToOmit, collection)).toEqual([ 'D', 'E', 'F' ])
  expect(without(itemsToOmit)(collection)).toEqual([ 'D', 'E', 'F' ])
})

test('with list of objects', () => {
  const itemsToOmit = [ { a : 1 }, { c : 3 } ]
  const collection = [ { a : 1 }, { b : 2 }, { c : 3 }, { d : 4 } ]
  const expected = [ { b : 2 }, { d : 4 } ]

  expect(without(itemsToOmit, collection)).toEqual(expected)
  expect(withoutRamda(itemsToOmit, collection)).toEqual(expected)
})

test('ramda accepts string as target input while rambda throws', () => {
  expect(withoutRamda('0:1', [ '0', '0:1' ])).toEqual([ '0:1' ])
  expect(() =>
    without('0:1', [ '0', '0:1' ])).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of 0:1"')
  expect(without([ '0:1' ], [ '0', '0:1' ])).toEqual([ '0' ])
})

test('ramda test', () => {
  expect(without([ 1, 2 ])([ 1, 2, 1, 3, 4 ])).toEqual([ 3, 4 ])
})

xnor

xnor(x: boolean, y: boolean): boolean

Logical XNOR

const result = [
  R.xnor(1, 0),
  R.xnor(0, 1),
  R.xnor(0, 0),
  R.xnor(1, 1),
]
// => [true, false, false, true]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.xnor(1%2C%200)%2C%0A%20%20R.xnor(0%2C%201)%2C%0A%20%20R.xnor(0%2C%200)%2C%0A%20%20R.xnor(1%2C%201)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%2C%20false%2C%20true%5D">Try this <strong>R.xnor</strong> example in Rambda REPL</a>

export function xnor(x, y){
  if (arguments.length === 1){
    return _y => xnor(x, _y)
  }

  return Boolean(x && y || !x && !y)
}

import { xnor } from './xnor.js'

test('when true', () => {
  expect(xnor(1, 1)).toBeTrue()
  expect(xnor(0)(0)).toBeTrue()
})

test('when false', () => {
  expect(xnor(0, 1)).toBeFalse()
})

xor

xor(x: boolean, y: boolean): boolean

Logical XOR

const result = [
  xor(true, true),
  xor(false, false),
  xor(false, true),
]
// => [false, false, true]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20xor(true%2C%20true)%2C%0A%20%20xor(false%2C%20false)%2C%0A%20%20xor(false%2C%20true)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20false%2C%20true%5D">Try this <strong>R.xor</strong> example in Rambda REPL</a>

export function xor(a, b){
  if (arguments.length === 1) return _b => xor(a, _b)

  return Boolean(a) && !b || Boolean(b) && !a
}

import { xor } from './xor.js'

test('compares two values with exclusive or', () => {
  expect(xor(true, true)).toBeFalse()
  expect(xor(true, false)).toBeTrue()
  expect(xor(false, true)).toBeTrue()
  expect(xor(false, false)).toBeFalse()
})

test('when both values are truthy, it should return false', () => {
  expect(xor(true, 'foo')).toBeFalse()
  expect(xor(42, true)).toBeFalse()
  expect(xor('foo', 42)).toBeFalse()
  expect(xor({}, true)).toBeFalse()
  expect(xor(true, [])).toBeFalse()
  expect(xor([], {})).toBeFalse()
  expect(xor(new Date(), true)).toBeFalse()
  expect(xor(true, Infinity)).toBeFalse()
  expect(xor(Infinity, new Date())).toBeFalse()
})

test('when both values are falsy, it should return false', () => {
  expect(xor(null, false)).toBeFalse()
  expect(xor(false, undefined)).toBeFalse()
  expect(xor(undefined, null)).toBeFalse()
  expect(xor(0, false)).toBeFalse()
  expect(xor(false, NaN)).toBeFalse()
  expect(xor(NaN, 0)).toBeFalse()
  expect(xor('', false)).toBeFalse()
})

test('when one argument is truthy and the other is falsy, it should return true', () => {
  expect(xor('foo', null)).toBeTrue()
  expect(xor(null, 'foo')).toBeTrue()
  expect(xor(undefined, 42)).toBeTrue()
  expect(xor(42, undefined)).toBeTrue()
  expect(xor(Infinity, NaN)).toBeTrue()
  expect(xor(NaN, Infinity)).toBeTrue()
  expect(xor({}, '')).toBeTrue()
  expect(xor('', {})).toBeTrue()
  expect(xor(new Date(), 0)).toBeTrue()
  expect(xor(0, new Date())).toBeTrue()
  expect(xor([], null)).toBeTrue()
  expect(xor(undefined, [])).toBeTrue()
})

zip

zip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[]

It will return a new array containing tuples of equally positions items from both x and y lists.

The returned list will be truncated to match the length of the shortest supplied list.

const x = [1, 2]
const y = ['A', 'B']
R.zip(x, y)
// => [[1, 'A'], [2, 'B']]

// truncates to shortest list
R.zip([...x, 3], ['A', 'B'])
// => [[1, 'A'], [2, 'B']]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%20%5B1%2C%202%5D%0Aconst%20y%20%3D%20%5B'A'%2C%20'B'%5D%0AR.zip(x%2C%20y)%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%20'A'%5D%2C%20%5B2%2C%20'B'%5D%5D%0A%0A%2F%2F%20truncates%20to%20shortest%20list%0Aconst%20result%20%3D%20R.zip(%5B...x%2C%203%5D%2C%20%5B'A'%2C%20'B'%5D)%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%20'A'%5D%2C%20%5B2%2C%20'B'%5D%5D">Try this <strong>R.zip</strong> example in Rambda REPL</a>

export function zip(left, right){
  if (arguments.length === 1) return _right => zip(left, _right)

  const result = []
  const length = Math.min(left.length, right.length)

  for (let i = 0; i < length; i++){
    result[ i ] = [ left[ i ], right[ i ] ]
  }

  return result
}

import { zip } from './zip.js'

const array1 = [ 1, 2, 3 ]
const array2 = [ 'A', 'B', 'C' ]

test('should return an array', () => {
  const actual = zip(array1)(array2)
  expect(actual).toBeInstanceOf(Array)
})

test('should return and array or tuples', () => {
  const expected = [
    [ 1, 'A' ],
    [ 2, 'B' ],
    [ 3, 'C' ],
  ]
  const actual = zip(array1, array2)
  expect(actual).toEqual(expected)
})

test('should truncate result to length of shorted input list', () => {
  const expectedA = [
    [ 1, 'A' ],
    [ 2, 'B' ],
  ]
  const actualA = zip([ 1, 2 ], array2)
  expect(actualA).toEqual(expectedA)

  const expectedB = [
    [ 1, 'A' ],
    [ 2, 'B' ],
  ]
  const actualB = zip(array1, [ 'A', 'B' ])
  expect(actualB).toEqual(expectedB)
})

zipObj

zipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T }

It will return a new object with keys of keys array and values of values array.

const keys = ['a', 'b', 'c']

R.zipObj(keys, [1, 2, 3])
// => {a: 1, b: 2, c: 3}

// truncates to shortest list
R.zipObj(keys, [1, 2])
// => {a: 1, b: 2}

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20keys%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%5D%0A%0AR.zipObj(keys%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0A%0A%2F%2F%20truncates%20to%20shortest%20list%0Aconst%20result%20%3D%20R.zipObj(keys%2C%20%5B1%2C%202%5D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20b%3A%202%7D">Try this <strong>R.zipObj</strong> example in Rambda REPL</a>

import { take } from './take.js'

export function zipObj(keys, values){
  if (arguments.length === 1) return yHolder => zipObj(keys, yHolder)

  return take(values.length, keys).reduce((
    prev, xInstance, i
  ) => {
    prev[ xInstance ] = values[ i ]

    return prev
  }, {})
}

import { equals } from './equals.js'
import { zipObj } from './zipObj.js'

test('zipObj', () => {
  expect(zipObj([ 'a', 'b', 'c' ], [ 1, 2, 3 ])).toEqual({
    a : 1,
    b : 2,
    c : 3,
  })
})

test('0', () => {
  expect(zipObj([ 'a', 'b' ])([ 1, 2, 3 ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('1', () => {
  expect(zipObj([ 'a', 'b', 'c' ])([ 1, 2 ])).toEqual({
    a : 1,
    b : 2,
  })
})

test('ignore extra keys', () => {
  const result = zipObj([ 'a', 'b', 'c', 'd', 'e', 'f' ], [ 1, 2, 3 ])
  const expected = {
    a : 1,
    b : 2,
    c : 3,
  }

  expect(equals(result, expected)).toBeTrue()
})

zipWith

zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[]

const list1 = [ 10, 20, 30, 40 ]
const list2 = [ 100, 200 ]

const result = R.zipWith(
  R.add, list1, list2
)
// => [110, 220]

<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list1%20%3D%20%5B%2010%2C%2020%2C%2030%2C%2040%20%5D%0Aconst%20list2%20%3D%20%5B%20100%2C%20200%20%5D%0A%0Aconst%20result%20%3D%20R.zipWith(%0A%20%20R.add%2C%20list1%2C%20list2%0A)%0A%2F%2F%20%3D%3E%20%5B110%2C%20220%5D">Try this <strong>R.zipWith</strong> example in Rambda REPL</a>

import { curry } from './curry.js'
import { take } from './take.js'

function zipWithFn(
  fn, x, y
){
  return take(x.length > y.length ? y.length : x.length, x).map((xInstance, i) => fn(xInstance, y[ i ]))
}

export const zipWith = curry(zipWithFn)

import { add } from './add.js'
import { zipWith } from './zipWith.js'

const list1 = [ 1, 2, 3 ]
const list2 = [ 10, 20, 30, 40 ]
const list3 = [ 100, 200 ]

test('when second list is shorter', () => {
  const result = zipWith(
    add, list1, list3
  )
  expect(result).toEqual([ 101, 202 ])
})

test('when second list is longer', () => {
  const result = zipWith(
    add, list1, list2
  )
  expect(result).toEqual([ 11, 22, 33 ])
})

❯ CHANGELOG

11.3.0

• Fix deno release

• Sync with Rambda version 9.4.0

11.2.0

• R.throttle TS typings now support no argument case for function input.

• Sync with Rambda version 9.3.0

11.1.1

Fix broken build due to changes to TypeScript definitions for lenses.

11.1.0

• Improve R.mapToObject types - Issue #96

• Sync with Rambda version 9.2.0

11.0.0

• Sync with Rambda version 9.1.0

• Change typings of R.lensEq to match Rambda-adjust typings

10.1.0

• Simplify TypeScript logic of R.pipeAsync/R.composeAsync/R.pipedAsync - MR #698

• Sync with Rambda version 8.6.0

10.0.0

• Sync with Rambda version 8.0.0

• Add R.omitPaths - Issue #681

• Add R.noop

9.1.1

Add missing fix for type: module imports.

9.1.0

• Sync with Rambda version 7.5.0

9.0.0

From this release, CHANGELOG will simply refer to the Rambda version linked to the release, instead of listing Rambda changes here as well. In this case, the version referring to this release is `

This is only part of the changelog. You can read the full text in CHANGELOG.md file.

❯ Additional info

Most influential contributors(in alphabetical order)

• @farwayer - improving performance in R.find, R.filter; give the idea how to make benchmarks more reliable;

• @thejohnfreeman - add R.assoc, R.chain;

• @peeja - add several methods and fix mutiple issues; provides great MR documentation

• @helmuthdu - add R.clone; help improve code style;

• @jpgorman - add R.zip, R.reject, R.without, R.addIndex;

• @ku8ar - add R.slice, R.propOr, R.identical, R.propIs and several math related methods; introduce the idea to display missing Ramda methods;

• @romgrk - add R.groupBy, R.indexBy, R.findLast, R.findLastIndex;

• @squidfunk - add R.assocPath, R.symmetricDifference, R.difference, R.intersperse;

• @synthet1c - add all lenses methods; add R.applySpec, R.converge;

• @vlad-zhukov - help with configuring Rollup, Babel; change export file to use ES module exports;

Rambda references

• Interview with Dejan Totef at SurviveJS blog

• Awesome functional Javascript programming libraries

• Overview of Rambda pros/cons

Links to Rambda

• awesome-fp-js

• Web Tools Weekly #280

• awesome-docsify

Deprecated from Used by section

• SAP's Cloud SDK - This repo doesn't uses Rambda since October/2020 commit that removes Rambda

My other libraries

Stargazers over time