Awesome
30 seconds of code
Curated collection of useful JavaScript snippets that you can understand in 30 seconds or less.
- Use <kbd>Ctrl</kbd> + <kbd>F</kbd> or <kbd>command</kbd> + <kbd>F</kbd> to search for a snippet.
- Contributions welcome, please read the contribution guide.
- Snippets are written in ES6, use the Babel transpiler to ensure backwards-compatibility.
- You can import these snippets into your text editor of choice (VSCode, Atom, Sublime) using the files found in this repo.
- You can import these snippets into Alfred 3, using this file.
Package
β οΈ WARNING: Snippets are not production ready.
You can find a package with all the snippets on npm.
# With npm
npm install 30-seconds-of-code
# With yarn
yarn add 30-seconds-of-code
CDN links
<details>Browser
IMPORTANT: replace the
src
with the full version link and desired target spec (such as ES5 minified)):
<script src="https://unpkg.com/30-seconds-of-code"></script>
<script>
_30s.average(1, 2, 3);
</script>
Node
// CommonJS
const _30s = require('30-seconds-of-code');
_30s.average(1, 2, 3);
// ES Modules
import _30s from '30-seconds-of-code';
_30s.average(1, 2, 3);
To import snippets directly:
// CommonJS
const { average } = require('30-seconds-of-code');
average(1, 2, 3);
// ES Modules
import { average } from '30-seconds-of-code';
average(1, 2, 3);
</details>
Table of Contents
π Adapter
<details> <summary>View contents</summary> </details>π Array
<details> <summary>View contents</summary>chunk
compact
countBy
countOccurrences
deepFlatten
difference
differenceWith
distinctValuesOfArray
dropElements
dropRight
everyNth
filterNonUnique
findLast
flatten
forEachRight
groupBy
head
indexOfAll
initial
initialize2DArray
initializeArrayWithRange
initializeArrayWithValues
intersection
isSorted
join
last
longestItem
mapObject
maxN
minN
nthElement
partition
pick
pull
pullAtIndex
pullAtValue
reducedFilter
remove
sample
sampleSize
shuffle
similarity
sortedIndex
symmetricDifference
tail
take
takeRight
union
without
zip
zipObject
π Browser
<details> <summary>View contents</summary>arrayToHtmlList
bottomVisible
copyToClipboard
createElement
createEventHub
currentURL
detectDeviceType
elementIsVisibleInViewport
getScrollPosition
getStyle
hasClass
hide
httpsRedirect
off
on
onUserInputChange
redirect
runAsync
scrollToTop
setStyle
show
toggleClass
UUIDGeneratorBrowser
β±οΈ Date
<details> <summary>View contents</summary> </details>ποΈ Function
<details> <summary>View contents</summary> </details>β Math
<details> <summary>View contents</summary>average
averageBy
clampNumber
digitize
distance
elo
factorial
fibonacci
gcd
geometricProgression
hammingDistance
inRange
isDivisible
isEven
isPrime
lcm
luhnCheck
maxBy
median
minBy
percentile
powerset
primes
randomIntArrayInRange
randomIntegerInRange
randomNumberInRange
round
sdbm
standardDeviation
sum
sumBy
sumPower
toSafeInteger
π¦ Node
<details> <summary>View contents</summary> </details>ποΈ Object
<details> <summary>View contents</summary>cleanObj
equals
functions
invertKeyValues
lowercaseKeys
mapKeys
mapValues
merge
objectFromPairs
objectToPairs
orderBy
select
shallowClone
size
transform
truthCheckCollection
π String
<details> <summary>View contents</summary>anagrams
byteSize
capitalize
capitalizeEveryWord
decapitalize
escapeHTML
escapeRegExp
fromCamelCase
isAbsoluteURL
isLowerCase
isUpperCase
mask
palindrome
pluralize
reverseString
sortCharactersInString
splitLines
toCamelCase
toKebabCase
toSnakeCase
truncateString
unescapeHTML
words
π Type
<details> <summary>View contents</summary>getType
isArray
isArrayLike
isBoolean
isFunction
isNull
isNumber
isObject
isPrimitive
isPromiseLike
isString
isSymbol
isValidJSON
π§ Utility
<details> <summary>View contents</summary>cloneRegExp
coalesce
coalesceFactory
extendHex
getURLParameters
hexToRGB
httpGet
httpPost
parseCookie
prettyBytes
randomHexColorCode
RGBToHex
serializeCookie
timeTaken
toDecimalMark
toOrdinalSuffix
validateNumber
yesNo
π Adapter
call
Given a key and a set of arguments, call them when given a context. Primarily useful in composition.
Use a closure to call a stored key with stored arguments.
const call = (key, ...args) => context => context[key](...args);
<details>
<summary>Examples</summary>
Promise.resolve([1, 2, 3])
.then(call('map', x => 2 * x))
.then(console.log); //[ 2, 4, 6 ]
const map = call.bind(null, 'map');
Promise.resolve([1, 2, 3])
.then(map(x => 2 * x))
.then(console.log); //[ 2, 4, 6 ]
</details>
<br>β¬ Back to top
collectInto
Changes a function that accepts an array into a variadic function.
Given a function, return a closure that collects all inputs into an array-accepting function.
const collectInto = fn => (...args) => fn(args);
<details>
<summary>Examples</summary>
const Pall = collectInto(Promise.all.bind(Promise));
let p1 = Promise.resolve(1);
let p2 = Promise.resolve(2);
let p3 = new Promise(resolve => setTimeout(resolve, 2000, 3));
Pall(p1, p2, p3).then(console.log);
</details>
<br>β¬ Back to top
flip
Flip takes a function as an argument, then makes the first argument the last.
Return a closure that takes variadic inputs, and splices the last argument to make it the first argument before applying the rest.
const flip = fn => (...args) => fn(args.pop(), ...args);
<details>
<summary>Examples</summary>
let a = { name: 'John Smith' };
let b = {};
const mergeFrom = flip(Object.assign);
let mergePerson = mergeFrom.bind(null, a);
mergePerson(b); // == b
b = {};
Object.assign(b, a); // == b
</details>
<br>β¬ Back to top
pipeFunctions
Performs left-to-right function composition.
Use Array.reduce()
with the spread operator (...
) to perform left-to-right function composition.
The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));
<details>
<summary>Examples</summary>
const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = pipeFunctions(multiply, add5);
multiplyAndAdd5(5, 2); // 15
</details>
<br>β¬ Back to top
promisify
Converts an asynchronous function to return a promise.
Use currying to return a function returning a Promise
that calls the original function.
Use the ...rest
operator to pass in all the parameters.
In Node 8+, you can use util.promisify
const promisify = func => (...args) =>
new Promise((resolve, reject) =>
func(...args, (err, result) => (err ? reject(err) : resolve(result)))
);
<details>
<summary>Examples</summary>
const delay = promisify((d, cb) => setTimeout(cb, d));
delay(2000).then(() => console.log('Hi!')); // // Promise resolves after 2s
</details>
<br>β¬ Back to top
spreadOver
Takes a variadic function and returns a closure that accepts an array of arguments to map to the inputs of the function.
Use closures and the spread operator (...
) to map the array of arguments to the inputs of the function.
const spreadOver = fn => argsArr => fn(...argsArr);
<details>
<summary>Examples</summary>
const arrayMax = spreadOver(Math.max);
arrayMax([1, 2, 3]); // 3
</details>
<br>β¬ Back to top
π Array
chunk
Chunks an array into smaller arrays of a specified size.
Use Array.from()
to create a new array, that fits the number of chunks that will be produced.
Use Array.slice()
to map each element of the new array to a chunk the length of size
.
If the original array can't be split evenly, the final chunk will contain the remaining elements.
const chunk = (arr, size) =>
Array.from({ length: Math.ceil(arr.length / size) }, (v, i) =>
arr.slice(i * size, i * size + size)
);
<details>
<summary>Examples</summary>
chunk([1, 2, 3, 4, 5], 2); // [[1,2],[3,4],[5]]
</details>
<br>β¬ Back to top
compact
Removes falsey values from an array.
Use Array.filter()
to filter out falsey values (false
, null
, 0
, ""
, undefined
, and NaN
).
const compact = arr => arr.filter(Boolean);
<details>
<summary>Examples</summary>
compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]); // [ 1, 2, 3, 'a', 's', 34 ]
</details>
<br>β¬ Back to top
countBy
Groups the elements of an array based on the given function and returns the count of elements in each group.
Use Array.map()
to map the values of an array to a function or property name.
Use Array.reduce()
to create an object, where the keys are produced from the mapped results.
const countBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
acc[val] = (acc[val] || 0) + 1;
return acc;
}, {});
<details>
<summary>Examples</summary>
countBy([6.1, 4.2, 6.3], Math.floor); // {4: 1, 6: 2}
countBy(['one', 'two', 'three'], 'length'); // {3: 2, 5: 1}
</details>
<br>β¬ Back to top
countOccurrences
Counts the occurrences of a value in an array.
Use Array.reduce()
to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a + 0), 0);
<details>
<summary>Examples</summary>
countOccurrences([1, 1, 2, 1, 2, 3], 1); // 3
</details>
<br>β¬ Back to top
deepFlatten
Deep flattens an array.
Use recursion.
Use Array.concat()
with an empty array ([]
) and the spread operator (...
) to flatten an array.
Recursively flatten each element that is an array.
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
<details>
<summary>Examples</summary>
deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]
</details>
<br>β¬ Back to top
difference
Returns the difference between two arrays.
Create a Set
from b
, then use Array.filter()
on a
to only keep values not contained in b
.
const difference = (a, b) => {
const s = new Set(b);
return a.filter(x => !s.has(x));
};
<details>
<summary>Examples</summary>
difference([1, 2, 3], [1, 2, 4]); // [3]
</details>
<br>β¬ Back to top
differenceWith
Filters out all values from an array for which the comparator function does not return true
.
Use Array.filter()
and Array.findIndex()
to find the appropriate values.
const differenceWith = (arr, val, comp) => arr.filter(a => val.findIndex(b => comp(a, b)) === -1);
<details>
<summary>Examples</summary>
differenceWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2]
</details>
<br>β¬ Back to top
distinctValuesOfArray
Returns all the distinct values of an array.
Use ES6 Set
and the ...rest
operator to discard all duplicated values.
const distinctValuesOfArray = arr => [...new Set(arr)];
<details>
<summary>Examples</summary>
distinctValuesOfArray([1, 2, 2, 3, 4, 4, 5]); // [1,2,3,4,5]
</details>
<br>β¬ Back to top
dropElements
Removes elements in an array until the passed function returns true
. Returns the remaining elements in the array.
Loop through the array, using Array.slice()
to drop the first element of the array until the returned value from the function is true
.
Returns the remaining elements.
const dropElements = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
return arr;
};
<details>
<summary>Examples</summary>
dropElements([1, 2, 3, 4], n => n >= 3); // [3,4]
</details>
<br>β¬ Back to top
dropRight
Returns a new array with n
elements removed from the right.
Use Array.slice()
to slice the remove the specified number of elements from the right.
const dropRight = (arr, n = 1) => arr.slice(0, -n);
<details>
<summary>Examples</summary>
dropRight([1, 2, 3]); // [1,2]
dropRight([1, 2, 3], 2); // [1]
dropRight([1, 2, 3], 42); // []
</details>
<br>β¬ Back to top
everyNth
Returns every nth element in an array.
Use Array.filter()
to create a new array that contains every nth element of a given array.
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1);
<details>
<summary>Examples</summary>
everyNth([1, 2, 3, 4, 5, 6], 2); // [ 2, 4, 6 ]
</details>
<br>β¬ Back to top
filterNonUnique
Filters out the non-unique values in an array.
Use Array.filter()
for an array containing only the unique values.
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
<details>
<summary>Examples</summary>
filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1,3,5]
</details>
<br>β¬ Back to top
findLast
Returns the last element for which the provided function returns a truthy value.
Use Array.filter()
to remove elements for which fn
returns falsey values, Array.slice(-1)
to get the last one.
const findLast = (arr, fn) => arr.filter(fn).slice(-1);
<details>
<summary>Examples</summary>
findLast([1, 2, 3, 4], n => n % 2 === 1); // 3
</details>
<br>β¬ Back to top
flatten
Flattens an array up to the specified depth.
Use recursion, decrementing depth
by 1 for each level of depth.
Use Array.reduce()
and Array.concat()
to merge elements or arrays.
Base case, for depth
equal to 1
stops recursion.
Omit the second argument, depth
to flatten only to a depth of 1
(single flatten).
const flatten = (arr, depth = 1) =>
depth != 1
? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flatten(v, depth - 1) : v), [])
: arr.reduce((a, v) => a.concat(v), []);
<details>
<summary>Examples</summary>
flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]
</details>
<br>β¬ Back to top
forEachRight
Executes a provided function once for each array element, starting from the array's last element.
Use Array.slice(0)
to clone the given array, Array.reverse()
to reverse it and Array.forEach()
to iterate over the reversed array.
const forEachRight = (arr, callback) =>
arr
.slice(0)
.reverse()
.forEach(callback);
<details>
<summary>Examples</summary>
forEachRight([1, 2, 3, 4], val => console.log(val)); // '4', '3', '2', '1'
</details>
<br>β¬ Back to top
groupBy
Groups the elements of an array based on the given function.
Use Array.map()
to map the values of an array to a function or property name.
Use Array.reduce()
to create an object, where the keys are produced from the mapped results.
const groupBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
acc[val] = (acc[val] || []).concat(arr[i]);
return acc;
}, {});
<details>
<summary>Examples</summary>
groupBy([6.1, 4.2, 6.3], Math.floor); // {4: [4.2], 6: [6.1, 6.3]}
groupBy(['one', 'two', 'three'], 'length'); // {3: ['one', 'two'], 5: ['three']}
</details>
<br>β¬ Back to top
head
Returns the head of a list.
Use arr[0]
to return the first element of the passed array.
const head = arr => arr[0];
<details>
<summary>Examples</summary>
head([1, 2, 3]); // 1
</details>
<br>β¬ Back to top
indexOfAll
Returns all indices of val
in an array. If val
never occurs, returns []
.
Use Array.forEach()
to loop over elements and Array.push()
to store indices for matching elements.
Return the array of indices.
const indexOfAll = (arr, val) => {
const indices = [];
arr.forEach((el, i) => el === val && indices.push(i));
return indices;
};
<details>
<summary>Examples</summary>
indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
indexOfAll([1, 2, 3], 4); // []
</details>
<br>β¬ Back to top
initial
Returns all the elements of an array except the last one.
Use arr.slice(0,-1)
to return all but the last element of the array.
const initial = arr => arr.slice(0, -1);
<details>
<summary>Examples</summary>
initial([1, 2, 3]); // [1,2]
</details>
<br>β¬ Back to top
initialize2DArray
Initializes a 2D array of given width and height and value.
Use Array.map()
to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null
.
const initialize2DArray = (w, h, val = null) =>
Array.from({ length: h }).map(() => Array.from({ length: w }).fill(val));
<details>
<summary>Examples</summary>
initialize2DArray(2, 2, 0); // [[0,0], [0,0]]
</details>
<br>β¬ Back to top
initializeArrayWithRange
Initializes an array containing the numbers in the specified range where start
and end
are inclusive with there common difference step
.
Use Array.from(Math.ceil((end+1-start)/step))
to create an array of the desired length(the amounts of elements is equal to (end-start)/step
or (end+1-start)/step
for inclusive end), Array.map()
to fill with the desired values in a range.
You can omit start
to use a default value of 0
.
You can omit step
to use a default value of 1
.
const initializeArrayWithRange = (end, start = 0, step = 1) =>
Array.from({ length: Math.ceil((end + 1 - start) / step) }).map((v, i) => i * step + start);
<details>
<summary>Examples</summary>
initializeArrayWithRange(5); // [0,1,2,3,4,5]
initializeArrayWithRange(7, 3); // [3,4,5,6,7]
initializeArrayWithRange(9, 0, 2); // [0,2,4,6,8]
</details>
<br>β¬ Back to top
initializeArrayWithValues
Initializes and fills an array with the specified values.
Use Array(n)
to create an array of the desired length, fill(v)
to fill it with the desired values.
You can omit val
to use a default value of 0
.
const initializeArrayWithValues = (n, val = 0) => Array(n).fill(val);
<details>
<summary>Examples</summary>
initializeArrayWithValues(5, 2); // [2,2,2,2,2]
</details>
<br>β¬ Back to top
intersection
Returns a list of elements that exist in both arrays.
Create a Set
from b
, then use Array.filter()
on a
to only keep values contained in b
.
const intersection = (a, b) => {
const s = new Set(b);
return a.filter(x => s.has(x));
};
<details>
<summary>Examples</summary>
intersection([1, 2, 3], [4, 3, 2]); // [2,3]
</details>
<br>β¬ Back to top
isSorted
Returns 1
if the array is sorted in ascending order, -1
if it is sorted in descending order or 0
if it is not sorted.
Calculate the ordering direction
for the first two elements.
Use Object.entries()
to loop over array objects and compare them in pairs.
Return 0
if the direction
changes or the direction
if the last element is reached.
const isSorted = arr => {
const direction = arr[0] > arr[1] ? -1 : 1;
for (let [i, val] of arr.entries())
if (i === arr.length - 1) return direction;
else if ((val - arr[i + 1]) * direction > 0) return 0;
};
<details>
<summary>Examples</summary>
isSorted([0, 1, 2, 2]); // 1
isSorted([4, 3, 2]); // -1
isSorted([4, 3, 5]); // 0
</details>
<br>β¬ Back to top
join
Joins all elements of an array into a string and returns this string. Uses a separator and an end separator.
Use Array.reduce()
to combine elements into a string.
Omit the second argument, separator
, to use a default separator of ','
.
Omit the third argument, end
, to use the same value as separator
by default.
const join = (arr, separator = ',', end = separator) =>
arr.reduce(
(acc, val, i) =>
i == arr.length - 2
? acc + val + end
: i == arr.length - 1 ? acc + val : acc + val + separator,
''
);
<details>
<summary>Examples</summary>
join(['pen', 'pineapple', 'apple', 'pen'], ',', '&'); // "pen,pineapple,apple&pen"
join(['pen', 'pineapple', 'apple', 'pen'], ','); // "pen,pineapple,apple,pen"
join(['pen', 'pineapple', 'apple', 'pen']); // "pen,pineapple,apple,pen"
</details>
<br>β¬ Back to top
last
Returns the last element in an array.
Use arr.length - 1
to compute the index of the last element of the given array and returning it.
const last = arr => arr[arr.length - 1];
<details>
<summary>Examples</summary>
last([1, 2, 3]); // 3
</details>
<br>β¬ Back to top
longestItem
Takes any number of iterable objects or objects with a length
property and returns the longest one.
Use Array.sort()
to sort all arguments by length
, return the first (longest) one.
const longestItem = (...vals) => [...vals].sort((a, b) => b.length - a.length)[0];
<details>
<summary>Examples</summary>
longestItem('this', 'is', 'a', 'testcase'); // 'testcase'
longestItem(...['a', 'ab', 'abc']); // 'abc'
longestItem(...['a', 'ab', 'abc'], 'abcd'); // 'abcd'
longestItem([1, 2, 3], [1, 2], [1, 2, 3, 4, 5]); // [1, 2, 3, 4, 5]
longestItem([1, 2, 3], 'foobar'); // 'foobar'
</details>
<br>β¬ Back to top
mapObject
Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.
Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array
to store the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).
const mapObject = (arr, fn) =>
(a => (
(a = [arr, arr.map(fn)]), a[0].reduce((acc, val, ind) => ((acc[val] = a[1][ind]), acc), {})
))();
<details>
<summary>Examples</summary>
const squareIt = arr => mapObject(arr, a => a * a);
squareIt([1, 2, 3]); // { 1: 1, 2: 4, 3: 9 }
</details>
<br>β¬ Back to top
maxN
Returns the n
maximum elements from the provided array. If n
is greater than or equal to the provided array's length, then return the original array(sorted in descending order).
Use Array.sort()
combined with the spread operator (...
) to create a shallow clone of the array and sort it in descending order.
Use Array.slice()
to get the specified number of elements.
Omit the second argument, n
, to get a one-element array.
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);
<details>
<summary>Examples</summary>
maxN([1, 2, 3]); // [3]
maxN([1, 2, 3], 2); // [3,2]
</details>
<br>β¬ Back to top
minN
Returns the n
minimum elements from the provided array. If n
is greater than or equal to the provided array's length, then return the original array(sorted in ascending order).
Use Array.sort()
combined with the spread operator (...
) to create a shallow clone of the array and sort it in ascending order.
Use Array.slice()
to get the specified number of elements.
Omit the second argument, n
, to get a one-element array.
const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n);
<details>
<summary>Examples</summary>
minN([1, 2, 3]); // [1]
minN([1, 2, 3], 2); // [1,2]
</details>
<br>β¬ Back to top
nthElement
Returns the nth element of an array.
Use Array.slice()
to get an array containing the nth element at the first place.
If the index is out of bounds, return []
.
Omit the second argument, n
, to get the first element of the array.
const nthElement = (arr, n = 0) => (n > 0 ? arr.slice(n, n + 1) : arr.slice(n))[0];
<details>
<summary>Examples</summary>
nthElement(['a', 'b', 'c'], 1); // 'b'
nthElement(['a', 'b', 'b'], -3); // 'a'
</details>
<br>β¬ Back to top
partition
Groups the elements into two arrays, depending on the provided function's truthiness for each element.
Use Array.reduce()
to create an array of two arrays.
Use Array.push()
to add elements for which fn
returns true
to the first array and elements for which fn
returns false
to the second one.
const partition = (arr, fn) =>
arr.reduce(
(acc, val, i, arr) => {
acc[fn(val, i, arr) ? 0 : 1].push(val);
return acc;
},
[[], []]
);
<details>
<summary>Examples</summary>
const users = [{ user: 'barney', age: 36, active: false }, { user: 'fred', age: 40, active: true }];
partition(users, o => o.active); // [[{ 'user': 'fred', 'age': 40, 'active': true }],[{ 'user': 'barney', 'age': 36, 'active': false }]]
</details>
<br>β¬ Back to top
pick
Picks the key-value pairs corresponding to the given keys from an object.
Use Array.reduce()
to convert the filtered/picked keys back to an object with the corresponding key-value pair if the key exists in the obj.
const pick = (obj, arr) =>
arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});
<details>
<summary>Examples</summary>
pick({ a: 1, b: '2', c: 3 }, ['a', 'c']); // { 'a': 1, 'c': 3 }
</details>
<br>β¬ Back to top
pull
Mutates the original array to filter out the values specified.
Use Array.filter()
and Array.includes()
to pull out the values that are not needed.
Use Array.length = 0
to mutate the passed in an array by resetting it's length to zero and Array.push()
to re-populate it with only the pulled values.
(For a snippet that does not mutate the original array see without
)
const pull = (arr, ...args) => {
let argState = Array.isArray(args[0]) ? args[0] : args;
let pulled = arr.filter((v, i) => !argState.includes(v));
arr.length = 0;
pulled.forEach(v => arr.push(v));
};
<details>
<summary>Examples</summary>
let myArray = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray, 'a', 'c'); // myArray = [ 'b', 'b' ]
</details>
<br>β¬ Back to top
pullAtIndex
Mutates the original array to filter out the values at the specified indexes.
Use Array.filter()
and Array.includes()
to pull out the values that are not needed.
Use Array.length = 0
to mutate the passed in an array by resetting it's length to zero and Array.push()
to re-populate it with only the pulled values.
Use Array.push()
to keep track of pulled values
const pullAtIndex = (arr, pullArr) => {
let removed = [];
let pulled = arr
.map((v, i) => (pullArr.includes(i) ? removed.push(v) : v))
.filter((v, i) => !pullArr.includes(i));
arr.length = 0;
pulled.forEach(v => arr.push(v));
return removed;
};
<details>
<summary>Examples</summary>
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtIndex(myArray, [1, 3]); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]
</details>
<br>β¬ Back to top
pullAtValue
Mutates the original array to filter out the values specified. Returns the removed elements.
Use Array.filter()
and Array.includes()
to pull out the values that are not needed.
Use Array.length = 0
to mutate the passed in an array by resetting it's length to zero and Array.push()
to re-populate it with only the pulled values.
Use Array.push()
to keep track of pulled values
const pullAtValue = (arr, pullArr) => {
let removed = [],
pushToRemove = arr.forEach((v, i) => (pullArr.includes(v) ? removed.push(v) : v)),
mutateTo = arr.filter((v, i) => !pullArr.includes(v));
arr.length = 0;
mutateTo.forEach(v => arr.push(v));
return removed;
};
<details>
<summary>Examples</summary>
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtValue(myArray, ['b', 'd']); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]
</details>
<br>β¬ Back to top
reducedFilter
Filter an array of objects based on a condition while also filtering out unspecified keys.
Use Array.filter()
to filter the array based on the predicate fn
so that it returns the objects for which the condition returned a truthy value.
On the filtered array, use Array.map()
to return the new object using Array.reduce()
to filter out the keys which were not supplied as the keys
argument.
const reducedFilter = (data, keys, fn) =>
data.filter(fn).map(el =>
keys.reduce((acc, key) => {
acc[key] = el[key];
return acc;
}, {})
);
<details>
<summary>Examples</summary>
const data = [
{
id: 1,
name: 'john',
age: 24
},
{
id: 2,
name: 'mike',
age: 50
}
];
reducedFilter(data, ['id', 'name'], item => item.age > 24); // [{ id: 2, name: 'mike'}]
</details>
<br>β¬ Back to top
remove
Removes elements from an array for which the given function returns false
.
Use Array.filter()
to find array elements that return truthy values and Array.reduce()
to remove elements using Array.splice()
.
The func
is invoked with three arguments (value, index, array
).
const remove = (arr, func) =>
Array.isArray(arr)
? arr.filter(func).reduce((acc, val) => {
arr.splice(arr.indexOf(val), 1);
return acc.concat(val);
}, [])
: [];
<details>
<summary>Examples</summary>
remove([1, 2, 3, 4], n => n % 2 == 0); // [2, 4]
</details>
<br>β¬ Back to top
sample
Returns a random element from an array.
Use Math.random()
to generate a random number, multiply it by length
and round it of to the nearest whole number using Math.floor()
.
This method also works with strings.
const sample = arr => arr[Math.floor(Math.random() * arr.length)];
<details>
<summary>Examples</summary>
sample([3, 7, 9, 11]); // 9
</details>
<br>β¬ Back to top
sampleSize
Gets n
random elements at unique keys from array
up to the size of array
.
Shuffle the array using the Fisher-Yates algorithm.
Use Array.slice()
to get the first n
elements.
Omit the second argument, n
to get only one element at random from the array.
const sampleSize = ([...arr], n = 1) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr.slice(0, n);
};
<details>
<summary>Examples</summary>
sampleSize([1, 2, 3], 2); // [3,1]
sampleSize([1, 2, 3], 4); // [2,3,1]
</details>
<br>β¬ Back to top
shuffle
Randomizes the order of the values of an array, returning a new array.
Uses the Fisher-Yates algorithm to reorder the elements of the array.
const shuffle = ([...arr]) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr;
};
<details>
<summary>Examples</summary>
const foo = [1, 2, 3];
shuffle(foo); // [2,3,1], foo = [1,2,3]
</details>
<br>β¬ Back to top
similarity
Returns an array of elements that appear in both arrays.
Use Array.filter()
to remove values that are not part of values
, determined using Array.includes()
.
const similarity = (arr, values) => arr.filter(v => values.includes(v));
<details>
<summary>Examples</summary>
similarity([1, 2, 3], [1, 2, 4]); // [1,2]
</details>
<br>β¬ Back to top
sortedIndex
Returns the lowest index at which value should be inserted into array in order to maintain its sort order.
Check if the array is sorted in descending order (loosely).
Use Array.findIndex()
to find the appropriate index where the element should be inserted.
const sortedIndex = (arr, n) => {
const isDescending = arr[0] > arr[arr.length - 1];
const index = arr.findIndex(el => (isDescending ? n >= el : n <= el));
return index === -1 ? arr.length : index;
};
<details>
<summary>Examples</summary>
sortedIndex([5, 3, 2, 1], 4); // 1
sortedIndex([30, 50], 40); // 1
</details>
<br>β¬ Back to top
symmetricDifference
Returns the symmetric difference between two arrays.
Create a Set
from each array, then use Array.filter()
on each of them to only keep values not contained in the other.
const symmetricDifference = (a, b) => {
const sA = new Set(a),
sB = new Set(b);
return [...a.filter(x => !sB.has(x)), ...b.filter(x => !sA.has(x))];
};
<details>
<summary>Examples</summary>
symmetricDifference([1, 2, 3], [1, 2, 4]); // [3,4]
</details>
<br>β¬ Back to top
tail
Returns all elements in an array except for the first one.
Return Array.slice(1)
if the array's length
is more than 1
, otherwise, return the whole array.
const tail = arr => (arr.length > 1 ? arr.slice(1) : arr);
<details>
<summary>Examples</summary>
tail([1, 2, 3]); // [2,3]
tail([1]); // [1]
</details>
<br>β¬ Back to top
take
Returns an array with n elements removed from the beginning.
Use Array.slice()
to create a slice of the array with n
elements taken from the beginning.
const take = (arr, n = 1) => arr.slice(0, n);
<details>
<summary>Examples</summary>
take([1, 2, 3], 5); // [1, 2, 3]
take([1, 2, 3], 0); // []
</details>
<br>β¬ Back to top
takeRight
Returns an array with n elements removed from the end.
Use Array.slice()
to create a slice of the array with n
elements taken from the end.
const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length);
<details>
<summary>Examples</summary>
takeRight([1, 2, 3], 2); // [ 2, 3 ]
takeRight([1, 2, 3]); // [3]
</details>
<br>β¬ Back to top
union
Returns every element that exists in any of the two arrays once.
Create a Set
with all values of a
and b
and convert to an array.
const union = (a, b) => Array.from(new Set([...a, ...b]));
<details>
<summary>Examples</summary>
union([1, 2, 3], [4, 3, 2]); // [1,2,3,4]
</details>
<br>β¬ Back to top
without
Filters out the elements of an array, that have one of the specified values.
Use Array.filter()
to create an array excluding(using !Array.includes()
) all given values.
(For a snippet that mutates the original array see pull
)
const without = (arr, ...args) => arr.filter(v => !args.includes(v));
<details>
<summary>Examples</summary>
without([2, 1, 2, 3], 1, 2); // [3]
</details>
<br>β¬ Back to top
zip
Creates an array of elements, grouped based on the position in the original arrays.
Use Math.max.apply()
to get the longest array in the arguments.
Creates an array with that length as return value and use Array.from()
with a map-function to create an array of grouped elements.
If lengths of the argument-arrays vary, undefined
is used where no value could be found.
const zip = (...arrays) => {
const maxLength = Math.max(...arrays.map(x => x.length));
return Array.from({ length: maxLength }).map((_, i) => {
return Array.from({ length: arrays.length }, (_, k) => arrays[k][i]);
});
};
<details>
<summary>Examples</summary>
zip(['a', 'b'], [1, 2], [true, false]); // [['a', 1, true], ['b', 2, false]]
zip(['a'], [1, 2], [true, false]); // [['a', 1, true], [undefined, 2, false]]
</details>
<br>β¬ Back to top
zipObject
Given an array of valid property identifiers and an array of values, return an object associating the properties to the values.
Since an object can have undefined values but not undefined property pointers, the array of properties is used to decide the structure of the resulting object using Array.reduce()
.
const zipObject = (props, values) =>
props.reduce((obj, prop, index) => ((obj[prop] = values[index]), obj), {});
<details>
<summary>Examples</summary>
zipObject(['a', 'b', 'c'], [1, 2]); // {a: 1, b: 2, c: undefined}
zipObject(['a', 'b'], [1, 2, 3]); // {a: 1, b: 2}
</details>
<br>β¬ Back to top
π Browser
arrayToHtmlList
Converts the given array elements into <li>
tags and appends them to the list of the given id.
Use Array.map()
and document.querySelector()
to create a list of html tags.
const arrayToHtmlList = (arr, listID) =>
arr.map(item => (document.querySelector('#' + listID).innerHTML += `<li>${item}</li>`));
<details>
<summary>Examples</summary>
arrayToHtmlList(['item 1', 'item 2'], 'myListID');
</details>
<br>β¬ Back to top
bottomVisible
Returns true
if the bottom of the page is visible, false
otherwise.
Use scrollY
, scrollHeight
and clientHeight
to determine if the bottom of the page is visible.
const bottomVisible = () =>
document.documentElement.clientHeight + window.scrollY >=
(document.documentElement.scrollHeight || document.documentElement.clientHeight);
<details>
<summary>Examples</summary>
bottomVisible(); // true
</details>
<br>β¬ Back to top
copyToClipboard
Copy a string to the clipboard. Only works as a result of user action (i.e. inside a click
event listener).
Create a new <textarea>
element, fill it with the supplied data and add it to the HTML document.
Use Selection.getRangeAt()
to store the selected range (if any).
Use document.execCommand('copy')
to copy to the clipboard.
Remove the <textarea>
element from the HTML document.
Finally, use Selection().addRange()
to recover the original selected range (if any).
const copyToClipboard = str => {
const el = document.createElement('textarea');
el.value = str;
el.setAttribute('readonly', '');
el.style.position = 'absolute';
el.style.left = '-9999px';
document.body.appendChild(el);
const selected =
document.getSelection().rangeCount > 0 ? document.getSelection().getRangeAt(0) : false;
el.select();
document.execCommand('copy');
document.body.removeChild(el);
if (selected) {
document.getSelection().removeAllRanges();
document.getSelection().addRange(selected);
}
};
<details>
<summary>Examples</summary>
copyToClipboard('Lorem ipsum'); // 'Lorem ipsum' copied to clipboard.
</details>
<br>β¬ Back to top
createElement
Creates an element from a string (without appending it to the document). If the given string contains multiple elements, only the first one will be returned.
Use document.createElement()
to create a new element.
Set its innerHTML
to the string supplied as the argument.
Use ParentNode.firstElementChild
to return the element version of the string.
const createElement = str => {
const el = document.createElement('div');
el.innerHTML = str;
return el.firstElementChild;
};
<details>
<summary>Examples</summary>
const el = createElement(
`<div class="container">
<p>Hello!</p>
</div>`
);
console.log(el.className); // 'container'
</details>
<br>β¬ Back to top
createEventHub
Creates a pub/sub (publishβsubscribe) event hub with emit
, on
, and off
methods.
Use Object.create(null)
to create an empty hub
object that does not inherit properties from Object.prototype
.
For emit
, resolve the array of handlers based on the event
argument and then run each one with Array.forEach()
by passing in the data as an argument.
For on
, create an array for the event if it does not yet exist, then use Array.push()
to add the handler
to the array.
For off
, use Array.findIndex()
to find the index of the handler in the event array and remove it using Array.splice()
.
const createEventHub = () => ({
hub: Object.create(null),
emit(event, data) {
(this.hub[event] || []).forEach(handler => handler(data));
},
on(event, handler) {
if (!this.hub[event]) this.hub[event] = [];
this.hub[event].push(handler);
},
off(event, handler) {
const i = (this.hub[event] || []).findIndex(h => h === handler);
if (i > -1) this.hub[event].splice(i, 1);
}
});
<details>
<summary>Examples</summary>
const handler = data => console.log(data);
const hub = createEventHub();
let increment = 0;
// Subscribe: listen for different types of events
hub.on('message', handler);
hub.on('message', () => console.log('Message event fired'));
hub.on('increment', () => increment++);
// Publish: emit events to invoke all handlers subscribed to them, passing the data to them as an argument
hub.emit('message', 'hello world'); // logs 'hello world' and 'Message event fired'
hub.emit('message', { hello: 'world' }); // logs the object and 'Message event fired'
hub.emit('increment'); // `increment` variable is now 1
// Unsubscribe: stop a specific handler from listening to the 'message' event
hub.off('message', handler);
</details>
<br>β¬ Back to top
currentURL
Returns the current URL.
Use window.location.href
to get current URL.
const currentURL = () => window.location.href;
<details>
<summary>Examples</summary>
currentURL(); // 'https://google.com'
</details>
<br>β¬ Back to top
detectDeviceType
Detects wether the website is being opened in a mobile device or a desktop/laptop.
Use a regular expression to test the navigator.userAgent
property to figure out if the device is a mobile device or a desktop/laptop.
const detectDeviceType = () =>
/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
? 'Mobile'
: 'Desktop';
<details>
<summary>Examples</summary>
detectDeviceType(); // "Mobile" or "Desktop"
</details>
<br>β¬ Back to top
elementIsVisibleInViewport
Returns true
if the element specified is visible in the viewport, false
otherwise.
Use Element.getBoundingClientRect()
and the window.inner(Width|Height)
values
to determine if a given element is visible in the viewport.
Omit the second argument to determine if the element is entirely visible, or specify true
to determine if
it is partially visible.
const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
const { top, left, bottom, right } = el.getBoundingClientRect();
const { innerHeight, innerWidth } = window;
return partiallyVisible
? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
: top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};
<details>
<summary>Examples</summary>
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
elementIsVisibleInViewport(el); // false - (not fully visible)
elementIsVisibleInViewport(el, true); // true - (partially visible)
</details>
<br>β¬ Back to top
getScrollPosition
Returns the scroll position of the current page.
Use pageXOffset
and pageYOffset
if they are defined, otherwise scrollLeft
and scrollTop
.
You can omit el
to use a default value of window
.
const getScrollPosition = (el = window) => ({
x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});
<details>
<summary>Examples</summary>
getScrollPosition(); // {x: 0, y: 200}
</details>
<br>β¬ Back to top
getStyle
Returns the value of a CSS rule for the specified element.
Use Window.getComputedStyle()
to get the value of the CSS rule for the specified element.
const getStyle = (el, ruleName) => getComputedStyle(el)[ruleName];
<details>
<summary>Examples</summary>
getStyle(document.querySelector('p'), 'font-size'); // '16px'
</details>
<br>β¬ Back to top
hasClass
Returns true
if the element has the specified class, false
otherwise.
Use element.classList.contains()
to check if the element has the specified class.
const hasClass = (el, className) => el.classList.contains(className);
<details>
<summary>Examples</summary>
hasClass(document.querySelector('p.special'), 'special'); // true
</details>
<br>β¬ Back to top
hide
Hides all the elements specified.
Use the spread operator (...
) and Array.forEach()
to apply display: none
to each element specified.
const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));
<details>
<summary>Examples</summary>
hide(...document.querySelectorAll('img')); // Hides all <img> elements on the page
</details>
<br>β¬ Back to top
httpsRedirect
Redirects the page to HTTPS if its currently in HTTP. Also, pressing the back button doesn't take it back to the HTTP page as its replaced in the history.
Use location.protocol
to get the protocol currently being used. If it's not HTTPS, use location.replace()
to replace the existing page with the HTTPS version of the page. Use location.href
to get the full address, split it with String.split()
and remove the protocol part of the URL.
const httpsRedirect = () => {
if (location.protocol !== 'https:') location.replace('https://' + location.href.split('//')[1]);
};
<details>
<summary>Examples</summary>
httpsRedirect(); // If you are on http://mydomain.com, you are redirected to https://mydomain.com
</details>
<br>β¬ Back to top
off
Removes an event listener from an element.
Use EventTarget.removeEventListener()
to remove an event listener from an element.
Omit the fourth argument opts
to use false
or specify it based on the options used when the event listener was added.
const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts);
<details>
<summary>Examples</summary>
const fn = () => console.log('!');
document.body.addEventListener('click', fn);
off(document.body, 'click', fn); // no longer logs '!' upon clicking on the page
</details>
<br>β¬ Back to top
on
Adds an event listener to an element with the ability to use event delegation.
Use EventTarget.addEventListener()
to add an event listener to an element. If there is a target
property supplied to the options object, ensure the event target matches the target specified and then invoke the callback by supplying the correct this
context.
Returns a reference to the custom delegator function, in order to be possible to use with off
.
Omit opts
to default to non-delegation behavior and event bubbling.
const on = (el, evt, fn, opts = {}) => {
const delegatorFn = e => e.target.matches(opts.target) && fn.call(e.target, e);
el.addEventListener(evt, opts.target ? delegatorFn : fn, opts.options || false);
if (opts.target) return delegatorFn;
};
<details>
<summary>Examples</summary>
const fn = () => console.log('!');
on(document.body, 'click', fn); // logs '!' upon clicking the body
on(document.body, 'click', fn, { target: 'p' }); // logs '!' upon clicking a `p` element child of the body
on(document.body, 'click', fn, { options: true }); // use capturing instead of bubbling
</details>
<br>β¬ Back to top
onUserInputChange
Run the callback whenever the user input type changes (mouse
or touch
). Useful for enabling/disabling code depending on the input device. This process is dynamic and works with hybrid devices (e.g. touchscreen laptops).
Use two event listeners. Assume mouse
input initially and bind a touchstart
event listener to the document.
On touchstart
, add a mousemove
event listener to listen for two consecutive mousemove
events firing within 20ms, using performance.now()
.
Run the callback with the input type as an argument in either of these situations.
const onUserInputChange = callback => {
let type = 'mouse',
lastTime = 0;
const mousemoveHandler = () => {
const now = performance.now();
if (now - lastTime < 20)
(type = 'mouse'), callback(type), document.removeEventListener('mousemove', mousemoveHandler);
lastTime = now;
};
document.addEventListener('touchstart', () => {
if (type === 'touch') return;
(type = 'touch'), callback(type), document.addEventListener('mousemove', mousemoveHandler);
});
};
<details>
<summary>Examples</summary>
onUserInputChange(type => {
console.log('The user is now using', type, 'as an input method.');
});
</details>
<br>β¬ Back to top
redirect
Redirects to a specified URL.
Use window.location.href
or window.location.replace()
to redirect to url
.
Pass a second argument to simulate a link click (true
- default) or an HTTP redirect (false
).
const redirect = (url, asLink = true) =>
asLink ? (window.location.href = url) : window.location.replace(url);
<details>
<summary>Examples</summary>
redirect('https://google.com');
</details>
<br>β¬ Back to top
runAsync
Runs a function in a separate thread by using a Web Worker, allowing long running functions to not block the UI.
Create a new Worker
using a Blob
object URL, the contents of which should be the stringified version of the supplied function.
Immediately post the return value of calling the function back.
Return a promise, listening for onmessage
and onerror
events and resolving the data posted back from the worker, or throwing an error.
const runAsync = fn => {
const blob = `var fn = ${fn.toString()}; postMessage(fn());`;
const worker = new Worker(
URL.createObjectURL(new Blob([blob]), {
type: 'application/javascript; charset=utf-8'
})
);
return new Promise((res, rej) => {
worker.onmessage = ({ data }) => {
res(data), worker.terminate();
};
worker.onerror = err => {
rej(err), worker.terminate();
};
});
};
<details>
<summary>Examples</summary>
const longRunningFunction = () => {
let result = 0;
for (let i = 0; i < 1000; i++) {
for (let j = 0; j < 700; j++) {
for (let k = 0; k < 300; k++) {
result = result + i + j + k;
}
}
}
return result;
};
/*
NOTE: Since the function is running in a different context, closures are not supported.
The function supplied to `runAsync` gets stringified, so everything becomes literal.
All variables and functions must be defined inside.
*/
runAsync(longRunningFunction).then(console.log); // 209685000000
runAsync(() => 10 ** 3).then(console.log); // 1000
let outsideVariable = 50;
runAsync(() => typeof outsideVariable).then(console.log); // 'undefined'
</details>
<br>β¬ Back to top
scrollToTop
Smooth-scrolls to the top of the page.
Get distance from top using document.documentElement.scrollTop
or document.body.scrollTop
.
Scroll by a fraction of the distance from the top. Use window.requestAnimationFrame()
to animate the scrolling.
const scrollToTop = () => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if (c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c / 8);
}
};
<details>
<summary>Examples</summary>
scrollToTop();
</details>
<br>β¬ Back to top
setStyle
Sets the value of a CSS rule for the specified element.
Use element.style
to set the value of the CSS rule for the specified element to val
.
const setStyle = (el, ruleName, val) => (el.style[ruleName] = val);
<details>
<summary>Examples</summary>
setStyle(document.querySelector('p'), 'font-size', '20px'); // The first <p> element on the page will have a font-size of 20px
</details>
<br>β¬ Back to top
show
Shows all the elements specified.
Use the spread operator (...
) and Array.forEach()
to clear the display
property for each element specified.
const show = (...el) => [...el].forEach(e => (e.style.display = ''));
<details>
<summary>Examples</summary>
show(...document.querySelectorAll('img')); // Shows all <img> elements on the page
</details>
<br>β¬ Back to top
toggleClass
Toggle a class for an element.
Use element.classList.toggle()
to toggle the specified class for the element.
const toggleClass = (el, className) => el.classList.toggle(className);
<details>
<summary>Examples</summary>
toggleClass(document.querySelector('p.special'), 'special'); // The paragraph will not have the 'special' class anymore
</details>
<br>β¬ Back to top
UUIDGeneratorBrowser
Generates a UUID in a browser.
Use crypto
API to generate a UUID, compliant with RFC4122 version 4.
const UUIDGeneratorBrowser = () =>
([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
(c ^ (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))).toString(16)
);
<details>
<summary>Examples</summary>
UUIDGeneratorBrowser(); // '7982fcfe-5721-4632-bede-6000885be57d'
</details>
<br>β¬ Back to top
β±οΈ Date
formatDuration
Returns the human readable format of the given number of milliseconds.
Divide ms
with the appropriate values to obtain the appropriate values for day
, hour
, minute
, second
and millisecond
.
Use Object.entries()
with Array.filter()
to keep only non-zero values.
Use Array.map()
to create the string for each value, pluralizing appropriately.
Use String.join(', ')
to combine the values into a string.
const formatDuration = ms => {
if (ms < 0) ms = -ms;
const time = {
day: Math.floor(ms / 86400000),
hour: Math.floor(ms / 3600000) % 24,
minute: Math.floor(ms / 60000) % 60,
second: Math.floor(ms / 1000) % 60,
millisecond: Math.floor(ms) % 1000
};
return Object.entries(time)
.filter(val => val[1] !== 0)
.map(val => val[1] + ' ' + (val[1] !== 1 ? val[0] + 's' : val[0]))
.join(', ');
};
<details>
<summary>Examples</summary>
formatDuration(1001); // '1 second, 1 millisecond'
formatDuration(34325055574); // '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'
</details>
<br>β¬ Back to top
getDaysDiffBetweenDates
Returns the difference (in days) between two dates.
Calculate the difference (in days) between two Date
objects.
const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
(dateFinal - dateInitial) / (1000 * 3600 * 24);
<details>
<summary>Examples</summary>
getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9
</details>
<br>β¬ Back to top
tomorrow
Results in a string representation of tomorrow's date.
Use new Date()
to get today's date, adding 86400000
of seconds to it(24 hours), using Date.toISOString()
to convert Date object to string.
const tomorrow = () => new Date(new Date().getTime() + 86400000).toISOString().split('T')[0];
<details>
<summary>Examples</summary>
tomorrow(); // 2017-12-27 (if current date is 2017-12-26)
</details>
<br>β¬ Back to top
ποΈ Function
chainAsync
Chains asynchronous functions.
Loop through an array of functions containing asynchronous events, calling next
when each asynchronous event has completed.
const chainAsync = fns => {
let curr = 0;
const next = () => fns[curr++](next);
next();
};
<details>
<summary>Examples</summary>
chainAsync([
next => {
console.log('0 seconds');
setTimeout(next, 1000);
},
next => {
console.log('1 second');
}
]);
</details>
<br>β¬ Back to top
compose
Performs right-to-left function composition.
Use Array.reduce()
to perform right-to-left function composition.
The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)));
<details>
<summary>Examples</summary>
const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = compose(add5, multiply);
multiplyAndAdd5(5, 2); // 15
</details>
<br>β¬ Back to top
curry
Curries a function.
Use recursion.
If the number of provided arguments (args
) is sufficient, call the passed function fn
.
Otherwise, return a curried function fn
that expects the rest of the arguments.
If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()
), you can optionally pass the number of arguments to the second parameter arity
.
const curry = (fn, arity = fn.length, ...args) =>
arity <= args.length ? fn(...args) : curry.bind(null, fn, arity, ...args);
<details>
<summary>Examples</summary>
curry(Math.pow)(2)(10); // 1024
curry(Math.min, 3)(10)(50)(2); // 2
</details>
<br>β¬ Back to top
defer
Defers invoking a function until the current call stack has cleared.
Use setTimeout()
with a timeout of 1ms to add a new event to the browser event queue and allow the rendering engine to complete its work. Use the spread (...
) operator to supply the function with an arbitrary number of arguments.
const defer = (fn, ...args) => setTimeout(fn, 1, ...args);
<details>
<summary>Examples</summary>
// Example A:
defer(console.log, 'a'), console.log('b'); // logs 'b' then 'a'
// Example B:
document.querySelector('#someElement').innerHTML = 'Hello';
longRunningFunction(); //Browser will not update the HTML until this has finished
defer(longRunningFunction); // Browser will update the HTML then run the function
</details>
<br>β¬ Back to top
functionName
Logs the name of a function.
Use console.debug()
and the name
property of the passed method to log the method's name to the debug
channel of the console.
const functionName = fn => (console.debug(fn.name), fn);
<details>
<summary>Examples</summary>
functionName(Math.max); // max (logged in debug channel of console)
</details>
<br>β¬ Back to top
memoize
Returns the memoized (cached) function.
Create an empty cache by instantiating a new Map
object.
Return a function which takes a single argument to be supplied to the memoized function by first checking if the function's output for that specific input value is already cached, or store and return it if not. The function
keyword must be used in order to allow the memoized function to have its this
context changed if necessary.
Allow access to the cache
by setting it as a property on the returned function.
const memoize = fn => {
const cache = new Map();
const cached = function(val) {
return cache.has(val) ? cache.get(val) : cache.set(val, fn.call(this, val)) && cache.get(val);
};
cached.cache = cache;
return cached;
};
<details>
<summary>Examples</summary>
// See the `anagrams` snippet.
const anagramsCached = memoize(anagrams);
anagramsCached('javascript'); // takes a long time
anagramsCached('javascript'); // returns virtually instantly since it's now cached
console.log(anagramsCached.cache); // The cached anagrams map
</details>
<br>β¬ Back to top
negate
Negates a predicate function.
Take a predicate function and apply the not operator (!
) to it with its arguments.
const negate = func => (...args) => !func(...args);
<details>
<summary>Examples</summary>
[1, 2, 3, 4, 5, 6].filter(negate(n => n % 2 == 0)); // [ 1, 3, 5 ]
</details>
<br>β¬ Back to top
once
Ensures a function is called only once.
Utilizing a closure, use a flag, called
, and set it to true
once the function is called for the first time, preventing it from being called again. In order to allow the function to have its this
context changed (such as in an event listener), the function
keyword must be used, and the supplied function must have the context applied.
Allow the function to be supplied with an arbitrary number of arguments using the rest/spread (...
) operator.
const once = fn => {
let called = false;
return function(...args) {
if (called) return;
called = true;
return fn.apply(this, args);
};
};
<details>
<summary>Examples</summary>
const startApp = function(event) {
console.log(this, event); // document.body, MouseEvent
};
document.body.addEventListener('click', once(startApp)); // only runs `startApp` once upon click
</details>
<br>β¬ Back to top
runPromisesInSeries
Runs an array of promises in series.
Use Array.reduce()
to create a promise chain, where each promise returns the next promise when resolved.
const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
<details>
<summary>Examples</summary>
const delay = d => new Promise(r => setTimeout(r, d));
runPromisesInSeries([() => delay(1000), () => delay(2000)]); // Executes each promise sequentially, taking a total of 3 seconds to complete
</details>
<br>β¬ Back to top
sleep
Delays the execution of an asynchronous function.
Delay executing part of an async
function, by putting it to sleep, returning a Promise
.
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
<details>
<summary>Examples</summary>
async function sleepyWork() {
console.log("I'm going to sleep for 1 second.");
await sleep(1000);
console.log('I woke up after 1 second.');
}
</details>
<br>β¬ Back to top
β Math
average
Returns the average of an of two or more numbers.
Use Array.reduce()
to add each value to an accumulator, initialized with a value of 0
, divide by the length
of the array.
const average = (...nums) => [...nums].reduce((acc, val) => acc + val, 0) / nums.length;
<details>
<summary>Examples</summary>
average(...[1, 2, 3]); // 2
average(1, 2, 3); // 2
</details>
<br>β¬ Back to top
averageBy
Returns the average of an array, after mapping each element to a value using the provided function.
Use Array.map()
to map each element to the value returned by fn
, Array.reduce()
to add each value to an accumulator, initialized with a value of 0
, divide by the length
of the array.
const averageBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0) /
arr.length;
<details>
<summary>Examples</summary>
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 5
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 5
</details>
<br>β¬ Back to top
clampNumber
Clamps num
within the inclusive range specified by the boundary values a
and b
.
If num
falls within the range, return num
.
Otherwise, return the nearest number in the range.
const clampNumber = (num, a, b) => Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));
<details>
<summary>Examples</summary>
clampNumber(2, 3, 5); // 3
clampNumber(1, -1, -5); // -1
</details>
<br>β¬ Back to top
digitize
Converts a number to an array of digits.
Convert the number to a string, using the spread operator (...
) to build an array.
Use Array.map()
and parseInt()
to transform each value to an integer.
const digitize = n => [...`${n}`].map(i => parseInt(i));
<details>
<summary>Examples</summary>
digitize(123); // [1, 2, 3]
</details>
<br>β¬ Back to top
distance
Returns the distance between two points.
Use Math.hypot()
to calculate the Euclidean distance between two points.
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
<details>
<summary>Examples</summary>
distance(1, 1, 2, 3); // 2.23606797749979
</details>
<br>β¬ Back to top
elo
Computes the new ratings between two or more opponents using the Elo rating system. It takes an array of pre-ratings and returns an array containing post-ratings. The array should be ordered from best performer to worst performer (winner -> loser).
Use the exponent **
operator and math operators to compute the expected score (chance of winning).
of each opponent and compute the new rating for each.
Loop through the ratings, using each permutation to compute the post-Elo rating for each player in a pairwise fashion.
Omit the second argument to use the default kFactor
of 32.
const elo = ([...ratings], kFactor = 32, selfRating) => {
const [a, b] = ratings;
const expectedScore = (self, opponent) => 1 / (1 + 10 ** ((opponent - self) / 400));
const newRating = (rating, i) =>
(selfRating || rating) + kFactor * (i - expectedScore(i ? a : b, i ? b : a));
if (ratings.length === 2) {
return [newRating(a, 1), newRating(b, 0)];
} else {
for (let i = 0; i < ratings.length; i++) {
let j = i;
while (j < ratings.length - 1) {
[ratings[i], ratings[j + 1]] = elo([ratings[i], ratings[j + 1]], kFactor);
j++;
}
}
}
return ratings;
};
<details>
<summary>Examples</summary>
// Standard 1v1s
elo([1200, 1200]); // [1216, 1184]
elo([1200, 1200], 64); // [1232, 1168]
// 4 player FFA, all same rank
elo([1200, 1200, 1200, 1200]).map(Math.round); // [1246, 1215, 1185, 1154]
/*
For teams, each rating can adjusted based on own team's average rating vs.
average rating of opposing team, with the score being added to their
own individual rating by supplying it as the third argument.
*/
</details>
<br>β¬ Back to top
factorial
Calculates the factorial of a number.
Use recursion.
If n
is less than or equal to 1
, return 1
.
Otherwise, return the product of n
and the factorial of n - 1
.
Throws an exception if n
is a negative number.
const factorial = n =>
n < 0
? (() => {
throw new TypeError('Negative numbers are not allowed!');
})()
: n <= 1 ? 1 : n * factorial(n - 1);
<details>
<summary>Examples</summary>
factorial(6); // 720
</details>
<br>β¬ Back to top
fibonacci
Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0
and 1
).
Use Array.reduce()
to add values into the array, using the sum of the last two values, except for the first two.
const fibonacci = n =>
Array.from({ length: n }).reduce(
(acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),
[]
);
<details>
<summary>Examples</summary>
fibonacci(6); // [0, 1, 1, 2, 3, 5]
</details>
<br>β¬ Back to top
gcd
Calculates the greatest common divisor between two or more numbers/arrays.
The inner _gcd
function uses recursion.
Base case is when y
equals 0
. In this case, return x
.
Otherwise, return the GCD of y
and the remainder of the division x/y
.
const gcd = (...arr) => {
const _gcd = (x, y) => (!y ? x : gcd(y, x % y));
return [...arr].reduce((a, b) => _gcd(a, b));
};
<details>
<summary>Examples</summary>
gcd(8, 36); // 4
gcd(...[12, 8, 32]); // 4
</details>
<br>β¬ Back to top
geometricProgression
Initializes an array containing the numbers in the specified range where start
and end
are inclusive and the ratio between two terms is step
.
Returns an error if step
equals 1
.
Use Array.from()
, Math.log()
and Math.floor()
to create an array of the desired length, Array.map()
to fill with the desired values in a range.
Omit the second argument, start
, to use a default value of 1
.
Omit the third argument, step
, to use a default value of 2
.
const geometricProgression = (end, start = 1, step = 2) =>
Array.from({ length: Math.floor(Math.log(end / start) / Math.log(step)) + 1 }).map(
(v, i) => start * step ** i
);
<details>
<summary>Examples</summary>
geometricProgression(256); // [1, 2, 4, 8, 16, 32, 64, 128, 256]
geometricProgression(256, 3); // [3, 6, 12, 24, 48, 96, 192]
geometricProgression(256, 1, 4); // [1, 4, 16, 64, 256]
</details>
<br>β¬ Back to top
hammingDistance
Calculates the Hamming distance between two values.
Use XOR operator (^
) to find the bit difference between the two numbers, convert to a binary string using toString(2)
.
Count and return the number of 1
s in the string, using match(/1/g)
.
const hammingDistance = (num1, num2) => ((num1 ^ num2).toString(2).match(/1/g) || '').length;
<details>
<summary>Examples</summary>
hammingDistance(2, 3); // 1
</details>
<br>β¬ Back to top
inRange
Checks if the given number falls within the given range.
Use arithmetic comparison to check if the given number is in the specified range.
If the second parameter, end
, is not specified, the range is considered to be from 0
to start
.
const inRange = (n, start, end = null) => {
if (end && start > end) end = [start, (start = end)][0];
return end == null ? n >= 0 && n < start : n >= start && n < end;
};
<details>
<summary>Examples</summary>
inRange(3, 2, 5); // true
inRange(3, 4); // true
inRange(2, 3, 5); // false
inrange(3, 2); // false
</details>
<br>β¬ Back to top
isDivisible
Checks if the first numeric argument is divisible by the second one.
Use the modulo operator (%
) to check if the remainder is equal to 0
.
const isDivisible = (dividend, divisor) => dividend % divisor === 0;
<details>
<summary>Examples</summary>
isDivisible(6, 3); // true
</details>
<br>β¬ Back to top
isEven
Returns true
if the given number is even, false
otherwise.
Checks whether a number is odd or even using the modulo (%
) operator.
Returns true
if the number is even, false
if the number is odd.
const isEven = num => num % 2 === 0;
<details>
<summary>Examples</summary>
isEven(3); // false
</details>
<br>β¬ Back to top
isPrime
Checks if the provided integer is a prime number.
Check numbers from 2
to the square root of the given number.
Return false
if any of them divides the given number, else return true
, unless the number is less than 2
.
const isPrime = num => {
const boundary = Math.floor(Math.sqrt(num));
for (var i = 2; i <= boundary; i++) if (num % i == 0) return false;
return num >= 2;
};
<details>
<summary>Examples</summary>
isPrime(11); // true
</details>
<br>β¬ Back to top
lcm
Returns the least common multiple of two or more numbers.
Use the greatest common divisor (GCD) formula and the fact that lcm(x,y) = x * y / gcd(x,y)
to determine the least common multiple.
The GCD formula uses recursion.
const lcm = (...arr) => {
const gcd = (x, y) => (!y ? x : gcd(y, x % y));
const _lcm = (x, y) => x * y / gcd(x, y);
return [...arr].reduce((a, b) => _lcm(a, b));
};
<details>
<summary>Examples</summary>
lcm(12, 7); // 84
lcm(...[1, 3, 4, 5]); // 60
</details>
<br>β¬ Back to top
luhnCheck
Implementation of the Luhn Algorithm used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers etc.
Use String.split('')
, Array.reverse()
and Array.map()
in combination with parseInt()
to obtain an array of digits.
Use Array.splice(0,1)
to obtain the last digit.
Use Array.reduce()
to implement the Luhn Algorithm.
Return true
if sum
is divisible by 10
, false
otherwise.
const luhnCheck = num => {
let arr = (num + '')
.split('')
.reverse()
.map(x => parseInt(x));
let lastDigit = arr.splice(0, 1)[0];
let sum = arr.reduce((acc, val, i) => (i % 2 !== 0 ? acc + val : acc + (val * 2) % 9 || 9), 0);
sum += lastDigit;
return sum % 10 === 0;
};
<details>
<summary>Examples</summary>
luhnCheck('4485275742308327'); // true
luhnCheck(6011329933655299); // false
luhnCheck(123456789); // false
</details>
<br>β¬ Back to top
maxBy
Returns the maximum value of an array, after mapping each element to a value using the provided function.
Use Array.map()
to map each element to the value returned by fn
, Math.max()
to get the maximum value.
const maxBy = (arr, fn) => Math.max(...arr.map(typeof fn === 'function' ? fn : val => val[fn]));
<details>
<summary>Examples</summary>
maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 8
maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 8
</details>
<br>β¬ Back to top
median
Returns the median of an array of numbers.
Find the middle of the array, use Array.sort()
to sort the values.
Return the number at the midpoint if length
is odd, otherwise the average of the two middle numbers.
const median = arr => {
const mid = Math.floor(arr.length / 2),
nums = [...arr].sort((a, b) => a - b);
return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};
<details>
<summary>Examples</summary>
median([5, 6, 50, 1, -5]); // 5
</details>
<br>β¬ Back to top
minBy
Returns the minimum value of an array, after mapping each element to a value using the provided function.
Use Array.map()
to map each element to the value returned by fn
, Math.min()
to get the maximum value.
const minBy = (arr, fn) => Math.min(...arr.map(typeof fn === 'function' ? fn : val => val[fn]));
<details>
<summary>Examples</summary>
minBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 8
minBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 8
</details>
<br>β¬ Back to top
percentile
Uses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.
Use Array.reduce()
to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.
const percentile = (arr, val) =>
100 * arr.reduce((acc, v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
<details>
<summary>Examples</summary>
percentile([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 6); // 55
</details>
<br>β¬ Back to top
powerset
Returns the powerset of a given array of numbers.
Use Array.reduce()
combined with Array.map()
to iterate over elements and combine into an array containing all combinations.
const powerset = arr => arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);
<details>
<summary>Examples</summary>
powerset([1, 2]); // [[], [1], [2], [2,1]]
</details>
<br>β¬ Back to top
primes
Generates primes up to a given number, using the Sieve of Eratosthenes.
Generate an array from 2
to the given number. Use Array.filter()
to filter out the values divisible by any number from 2
to the square root of the provided number.
const primes = num => {
let arr = Array.from({ length: num - 1 }).map((x, i) => i + 2),
sqroot = Math.floor(Math.sqrt(num)),
numsTillSqroot = Array.from({ length: sqroot - 1 }).map((x, i) => i + 2);
numsTillSqroot.forEach(x => (arr = arr.filter(y => y % x !== 0 || y == x)));
return arr;
};
<details>
<summary>Examples</summary>
primes(10); // [2,3,5,7]
</details>
<br>β¬ Back to top
randomIntArrayInRange
Returns an array of n random integers in the specified range.
Use Array.from()
to create an empty array of the specific length, Math.random()
to generate a random number and map it to the desired range, using Math.floor()
to make it an integer.
const randomIntArrayInRange = (min, max, n = 1) =>
Array.from({ length: n }, () => Math.floor(Math.random() * (max - min + 1)) + min);
<details>
<summary>Examples</summary>
randomIntArrayInRange(12, 35, 10); // [ 34, 14, 27, 17, 30, 27, 20, 26, 21, 14 ]
</details>
<br>β¬ Back to top
randomIntegerInRange
Returns a random integer in the specified range.
Use Math.random()
to generate a random number and map it to the desired range, using Math.floor()
to make it an integer.
const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
<details>
<summary>Examples</summary>
randomIntegerInRange(0, 5); // 2
</details>
<br>β¬ Back to top
randomNumberInRange
Returns a random number in the specified range.
Use Math.random()
to generate a random value, map it to the desired range using multiplication.
const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;
<details>
<summary>Examples</summary>
randomNumberInRange(2, 10); // 6.0211363285087005
</details>
<br>β¬ Back to top
round
Rounds a number to a specified amount of digits.
Use Math.round()
and template literals to round the number to the specified number of digits.
Omit the second argument, decimals
to round to an integer.
const round = (n, decimals = 0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);
<details>
<summary>Examples</summary>
round(1.005, 2); // 1.01
</details>
<br>β¬ Back to top
sbdm
Hashes the input string into a whole number.
Use String.split('')
and Array.reduce()
to create a hash of the input string, utilizing bit shifting.
const sdbm = str => {
let arr = str.split('');
return arr.reduce(
(hashCode, currentVal) =>
(hashCode = currentVal.charCodeAt(0) + (hashCode << 6) + (hashCode << 16) - hashCode),
0
);
};
<details>
<summary>Examples</summary>
sdbm('name'); // -3521204949
</details>
<br>β¬ Back to top
standardDeviation
Returns the standard deviation of an array of numbers.
Use Array.reduce()
to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then
determine the standard deviation.
You can omit the second argument to get the sample standard deviation or set it to true
to get the population standard deviation.
const standardDeviation = (arr, usePopulation = false) => {
const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
return Math.sqrt(
arr.reduce((acc, val) => acc.concat((val - mean) ** 2), []).reduce((acc, val) => acc + val, 0) /
(arr.length - (usePopulation ? 0 : 1))
);
};
<details>
<summary>Examples</summary>
standardDeviation([10, 2, 38, 23, 38, 23, 21]); // 13.284434142114991 (sample)
standardDeviation([10, 2, 38, 23, 38, 23, 21], true); // 12.29899614287479 (population)
</details>
<br>β¬ Back to top
sum
Returns the sum of two or more numbers/arrays.
Use Array.reduce()
to add each value to an accumulator, initialized with a value of 0
.
const sum = (...arr) => [...arr].reduce((acc, val) => acc + val, 0);
<details>
<summary>Examples</summary>
sum(...[1, 2, 3, 4]); // 10
</details>
<br>β¬ Back to top
sumBy
Returns the sum of an array, after mapping each element to a value using the provided function.
Use Array.map()
to map each element to the value returned by fn
, Array.reduce()
to add each value to an accumulator, initialized with a value of 0
.
const sumBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0);
<details>
<summary>Examples</summary>
sumBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 20
sumBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 20
</details>
<br>β¬ Back to top
sumPower
Returns the sum of the powers of all the numbers from start
to end
(both inclusive).
Use Array.fill()
to create an array of all the numbers in the target range, Array.map()
and the exponent operator (**
) to raise them to power
and Array.reduce()
to add them together.
Omit the second argument, power
, to use a default power of 2
.
Omit the third argument, start
, to use a default starting value of 1
.
const sumPower = (end, power = 2, start = 1) =>
Array(end + 1 - start)
.fill(0)
.map((x, i) => (i + start) ** power)
.reduce((a, b) => a + b, 0);
<details>
<summary>Examples</summary>
sumPower(10); // 385
sumPower(10, 3); //3025
sumPower(10, 3, 5); //2925
</details>
<br>β¬ Back to top
toSafeInteger
Converts a value to a safe integer.
Use Math.max()
and Math.min()
to find the closest safe value.
Use Math.round()
to convert to an integer.
const toSafeInteger = num =>
Math.round(Math.max(Math.min(num, Number.MAX_SAFE_INTEGER), Number.MIN_SAFE_INTEGER));
<details>
<summary>Examples</summary>
toSafeInteger('3.2'); // 3
toSafeInteger(Infinity); // 9007199254740991
</details>
<br>β¬ Back to top
π¦ Node
colorize
Add special characters to text to print in color in the console (combined with console.log()
).
Use template literals and special characters to add the appropriate color code to the string output. For background colors, add a special character that resets the background color at the end of the string.
const colorize = (...args) => ({
black: `\x1b[30m${args.join(' ')}`,
red: `\x1b[31m${args.join(' ')}`,
green: `\x1b[32m${args.join(' ')}`,
yellow: `\x1b[33m${args.join(' ')}`,
blue: `\x1b[34m${args.join(' ')}`,
magenta: `\x1b[35m${args.join(' ')}`,
cyan: `\x1b[36m${args.join(' ')}`,
white: `\x1b[37m${args.join(' ')}`,
bgBlack: `\x1b[40m${args.join(' ')}\x1b[0m`,
bgRed: `\x1b[41m${args.join(' ')}\x1b[0m`,
bgGreen: `\x1b[42m${args.join(' ')}\x1b[0m`,
bgYellow: `\x1b[43m${args.join(' ')}\x1b[0m`,
bgBlue: `\x1b[44m${args.join(' ')}\x1b[0m`,
bgMagenta: `\x1b[45m${args.join(' ')}\x1b[0m`,
bgCyan: `\x1b[46m${args.join(' ')}\x1b[0m`,
bgWhite: `\x1b[47m${args.join(' ')}\x1b[0m`
});
<details>
<summary>Examples</summary>
console.log(colorize('foo').red); // 'foo' (red letters)
console.log(colorize('foo', 'bar').bgBlue); // 'foo bar' (blue background)
console.log(colorize(colorize('foo').yellow, colorize('foo').green).bgWhite); // 'foo bar' (first word in yellow letters, second word in green letters, white background for both)
</details>
<br>β¬ Back to top
hasFlags
Check if the current process's arguments contain the specified flags.
Use Array.every()
and Array.includes()
to check if process.argv
contains all the specified flags.
Use a regular expression to test if the specified flags are prefixed with -
or --
and prefix them accordingly.
const hasFlags = (...flags) =>
flags.every(flag => process.argv.includes(/^-{1,2}/.test(flag) ? flag : '--' + flag));
<details>
<summary>Examples</summary>
// node myScript.js -s --test --cool=true
hasFlags('-s'); // true
hasFlags('--test', 'cool=true', '-s'); // true
hasFlags('special'); // false
</details>
<br>β¬ Back to top
isTravisCI
Checks if the current environment is Travis CI.
Checks if the current environment has the TRAVIS
and CI
environment variables (reference).
const isTravisCI = () => 'TRAVIS' in process.env && 'CI' in process.env;
<details>
<summary>Examples</summary>
isTravisCI(); // true (if code is running on Travis CI)
</details>
<br>β¬ Back to top
JSONToFile
Writes a JSON object to a file.
Use fs.writeFile()
, template literals and JSON.stringify()
to write a json
object to a .json
file.
const fs = require('fs');
const JSONToFile = (obj, filename) =>
fs.writeFile(`${filename}.json`, JSON.stringify(obj, null, 2));
<details>
<summary>Examples</summary>
JSONToFile({ test: 'is passed' }, 'testJsonFile'); // writes the object to 'testJsonFile.json'
</details>
<br>β¬ Back to top
readFileLines
Returns an array of lines from the specified file.
Use readFileSync
function in fs
node package to create a Buffer
from a file.
convert buffer to string using toString(encoding)
function.
creating an array from contents of file by split
ing file content line by line (each \n
).
const fs = require('fs');
const readFileLines = filename =>
fs
.readFileSync(filename)
.toString('UTF8')
.split('\n');
<details>
<summary>Examples</summary>
/*
contents of test.txt :
line1
line2
line3
___________________________
*/
let arr = readFileLines('test.txt');
console.log(arr); // ['line1', 'line2', 'line3']
</details>
<br>β¬ Back to top
untildify
Converts a tilde path to an absolute path.
Use String.replace()
with a regular expression and OS.homedir()
to replace the ~
in the start of the path with the home directory.
const untildify = str => str.replace(/^~($|\/|\\)/, `${require('os').homedir()}$1`);
<details>
<summary>Examples</summary>
untildify('~/node'); // '/Users/aUser/node'
</details>
<br>β¬ Back to top
UUIDGeneratorNode
Generates a UUID in Node.JS.
Use crypto
API to generate a UUID, compliant with RFC4122 version 4.
const crypto = require('crypto');
const UUIDGeneratorNode = () =>
([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
(c ^ (crypto.randomBytes(1)[0] & (15 >> (c / 4)))).toString(16)
);
<details>
<summary>Examples</summary>
UUIDGeneratorNode(); // '79c7c136-60ee-40a2-beb2-856f1feabefc'
</details>
<br>β¬ Back to top
ποΈ Object
cleanObj
Removes any properties except the ones specified from a JSON object.
Use Object.keys()
method to loop over given JSON object and deleting keys that are not included in given array.
If you pass a special key,childIndicator
, it will search deeply apply the function to inner objects, too.
const cleanObj = (obj, keysToKeep = [], childIndicator) => {
Object.keys(obj).forEach(key => {
if (key === childIndicator) {
cleanObj(obj[key], keysToKeep, childIndicator);
} else if (!keysToKeep.includes(key)) {
delete obj[key];
}
});
return obj;
};
<details>
<summary>Examples</summary>
const testObj = { a: 1, b: 2, children: { a: 1, b: 2 } };
cleanObj(testObj, ['a'], 'children'); // { a: 1, children : { a: 1}}
</details>
<br>β¬ Back to top
equals
Performs a deep comparison between two values to determine if they are equivalent.
Check if the two values are identical, if they are both Date
objects with the same time, using Date.getTime()
or if they are both non-object values with an equivalent value (strict comparison).
Check if only one value is null
or undefined
or if their prototypes differ.
If none of the above conditions are met, use Object.keys()
to check if both values have the same number of keys, then use Array.every()
to check if every key in the first value exists in the second one and if they are equivalent by calling this method recursively.
const equals = (a, b) => {
if (a === b) return true;
if (a instanceof Date && b instanceof Date) return a.getTime() === b.getTime();
if (!a || !b || (typeof a != 'object' && typeof b !== 'object')) return a === b;
if (a === null || a === undefined || b === null || b === undefined) return false;
if (a.prototype !== b.prototype) return false;
let keys = Object.keys(a);
if (keys.length !== Object.keys(b).length) return false;
return keys.every(k => equals(a[k], b[k]));
};
<details>
<summary>Examples</summary>
equals({ a: [2, { e: 3 }], b: [4], c: 'foo' }, { a: [2, { e: 3 }], b: [4], c: 'foo' }); // true
</details>
<br>β¬ Back to top
functions
Returns an array of function property names from own (and optionally inherited) enumerable properties of an object.
Use Object.keys(obj)
to iterate over the object's own properties.
If inherited
is true
, use Object.get.PrototypeOf(obj)
to also get the object's inherited properties.
Use Array.filter()
to keep only those properties that are functions.
Omit the second argument, inherited
, to not include inherited properties by default.
const functions = (obj, inherited = false) =>
(inherited
? [...Object.keys(obj), ...Object.keys(Object.getPrototypeOf(obj))]
: Object.keys(obj)
).filter(key => typeof obj[key] === 'function');
<details>
<summary>Examples</summary>
function Foo() {
this.a = () => 1;
this.b = () => 2;
}
Foo.prototype.c = () => 3;
functions(new Foo()); // ['a', 'b']
functions(new Foo(), true); // ['a', 'b', 'c']
</details>
<br>β¬ Back to top
invertKeyValues
Inverts the key-value pairs of an object, without mutating it.
Use Object.keys()
and Array.reduce()
to invert the key-value pairs of an object.
const invertKeyValues = obj =>
Object.keys(obj).reduce((acc, key) => {
acc[obj[key]] = key;
return acc;
}, {});
<details>
<summary>Examples</summary>
invertKeyValues({ name: 'John', age: 20 }); // { 20: 'age', John: 'name' }
</details>
<br>β¬ Back to top
lowercaseKeys
Creates a new object from the specified object, where all the keys are in lowercase.
Use Object.keys()
and Array.reduce()
to create a new object from the specified object.
Convert each key in the original object to lowercase, using String.toLowerCase()
.
const lowercaseKeys = obj =>
Object.keys(obj).reduce((acc, key) => {
acc[key.toLowerCase()] = obj[key];
return acc;
}, {});
<details>
<summary>Examples</summary>
const myObj = { Name: 'Adam', sUrnAME: 'Smith' };
const myObjLower = lowercaseKeys(myObj); // {name: 'Adam', surname: 'Smith'};
</details>
<br>β¬ Back to top
mapKeys
Creates an object with keys generated by running the provided function for each key and the same values as the provided object.
Use Object.keys(obj)
to iterate over the object's keys.
Use Array.reduce()
to create a new object with the same values and mapped keys using fn
.
const mapKeys = (obj, fn) =>
Object.keys(obj).reduce((acc, k) => {
acc[fn(obj[k], k, obj)] = obj[k];
return acc;
}, {});
<details>
<summary>Examples</summary>
mapKeys({ a: 1, b: 2 }, (val, key) => key + val); // { a1: 1, b2: 2 }
</details>
<br>β¬ Back to top
mapValues
Creates an object with the same keys as the provided object and values generated by running the provided function for each value.
Use Object.keys(obj)
to iterate over the object's keys.
Use Array.reduce()
to create a new object with the same keys and mapped values using fn
.
const mapValues = (obj, fn) =>
Object.keys(obj).reduce((acc, k) => {
acc[k] = fn(obj[k], k, obj);
return acc;
}, {});
<details>
<summary>Examples</summary>
const users = {
fred: { user: 'fred', age: 40 },
pebbles: { user: 'pebbles', age: 1 }
};
mapValues(users, u => u.age); // { fred: 40, pebbles: 1 }
</details>
<br>β¬ Back to top
merge
Creates a new object from the combination of two or more objects.
Use Array.reduce()
combined with Object.keys(obj)
to iterate over all objects and keys.
Use hasOwnProperty()
and Array.concat()
to append values for keys existing in multiple objects.
const merge = (...objs) =>
[...objs].reduce(
(acc, obj) =>
Object.keys(obj).reduce((a, k) => {
acc[k] = acc.hasOwnProperty(k) ? [].concat(acc[k]).concat(obj[k]) : obj[k];
return acc;
}, {}),
{}
);
<details>
<summary>Examples</summary>
const object = {
a: [{ x: 2 }, { y: 4 }],
b: 1
};
const other = {
a: { z: 3 },
b: [2, 3],
c: 'foo'
};
merge(object, other); // { a: [ { x: 2 }, { y: 4 }, { z: 3 } ], b: [ 1, 2, 3 ], c: 'foo' }
</details>
<br>β¬ Back to top
objectFromPairs
Creates an object from the given key-value pairs.
Use Array.reduce()
to create and combine key-value pairs.
const objectFromPairs = arr => arr.reduce((a, v) => ((a[v[0]] = v[1]), a), {});
<details>
<summary>Examples</summary>
objectFromPairs([['a', 1], ['b', 2]]); // {a: 1, b: 2}
</details>
<br>β¬ Back to top
objectToPairs
Creates an array of key-value pair arrays from an object.
Use Object.keys()
and Array.map()
to iterate over the object's keys and produce an array with key-value pairs.
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
<details>
<summary>Examples</summary>
objectToPairs({ a: 1, b: 2 }); // [['a',1],['b',2]]
</details>
<br>β¬ Back to top
orderBy
Returns a sorted array of objects ordered by properties and orders.
Uses Array.sort()
, Array.reduce()
on the props
array with a default value of 0
, use array destructuring to swap the properties position depending on the order passed.
If no orders
array is passed it sort by 'asc'
by default.
const orderBy = (arr, props, orders) =>
[...arr].sort((a, b) =>
props.reduce((acc, prop, i) => {
if (acc === 0) {
const [p1, p2] = orders && orders[i] === 'desc' ? [b[prop], a[prop]] : [a[prop], b[prop]];
acc = p1 > p2 ? 1 : p1 < p2 ? -1 : 0;
}
return acc;
}, 0)
);
<details>
<summary>Examples</summary>
const users = [{ name: 'fred', age: 48 }, { name: 'barney', age: 36 }, { name: 'fred', age: 40 }];
orderBy(users, ['name', 'age'], ['asc', 'desc']); // [{name: 'barney', age: 36}, {name: 'fred', age: 48}, {name: 'fred', age: 40}]
orderBy(users, ['name', 'age']); // [{name: 'barney', age: 36}, {name: 'fred', age: 40}, {name: 'fred', age: 48}]
</details>
<br>β¬ Back to top
select
Retrieve a set of properties indicated by the given selectors from an object.
Use Array.map()
for each selector, String.split('.')
to split each selector and Array.reduce()
to get the value indicated by it.
const select = (from, ...selectors) =>
[...selectors].map(s => s.split('.').reduce((prev, cur) => prev && prev[cur], from));
<details>
<summary>Examples</summary>
const obj = { selector: { to: { val: 'val to select' } } };
select(obj, 'selector.to.val'); // ['val to select']
select(obj, 'selector.to.val', 'selector.to'); // ['val to select', { val: 'val to select' }]
</details>
<br>β¬ Back to top
shallowClone
Creates a shallow clone of an object.
Use Object.assign()
and an empty object ({}
) to create a shallow clone of the original.
const shallowClone = obj => Object.assign({}, obj);
<details>
<summary>Examples</summary>
const a = { x: true, y: 1 };
const b = shallowClone(a); // a !== b
</details>
<br>β¬ Back to top
size
Get size of arrays, objects or strings.
Get type of val
(array
, object
or string
).
Use length
property for arrays.
Use length
or size
value if available or number of keys for objects.
Use size
of a Blob
object created from val
for strings.
Split strings into array of characters with split('')
and return its length.
const size = val =>
Array.isArray(val)
? val.length
: val && typeof val === 'object'
? val.size || val.length || Object.keys(val).length
: typeof val === 'string' ? new Blob([val]).size : 0;
<details>
<summary>Examples</summary>
size([1, 2, 3, 4, 5]); // 5
size('size'); // 4
size({ one: 1, two: 2, three: 3 }); // 3
</details>
<br>β¬ Back to top
transform
Applies a function against an accumulator and each key in the object (from left to right).
Use Object.keys(obj)
to iterate over each key in the object, Array.reduce()
to call the apply the specified function against the given accumulator.
const transform = (obj, fn, acc) => Object.keys(obj).reduce((a, k) => fn(a, obj[k], k, obj), acc);
<details>
<summary>Examples</summary>
transform(
{ a: 1, b: 2, c: 1 },
(r, v, k) => {
(r[v] || (r[v] = [])).push(k);
return r;
},
{}
); // { '1': ['a', 'c'], '2': ['b'] }
</details>
<br>β¬ Back to top
truthCheckCollection
Checks if the predicate (second argument) is truthy on all elements of a collection (first argument).
Use Array.every()
to check if each passed object has the specified property and if it returns a truthy value.
const truthCheckCollection = (collection, pre) => collection.every(obj => obj[pre]);
<details>
<summary>Examples</summary>
truthCheckCollection([{ user: 'Tinky-Winky', sex: 'male' }, { user: 'Dipsy', sex: 'male' }], 'sex'); // true
</details>
<br>β¬ Back to top
π String
anagrams
β οΈ WARNING: This function's execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your browser to hang as it tries to solve all the different combinations.
Generates all anagrams of a string (contains duplicates).
Use recursion.
For each letter in the given string, create all the partial anagrams for the rest of its letters.
Use Array.map()
to combine the letter with each partial anagram, then Array.reduce()
to combine all anagrams in one array.
Base cases are for string length
equal to 2
or 1
.
const anagrams = str => {
if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
return str
.split('')
.reduce(
(acc, letter, i) =>
acc.concat(anagrams(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)),
[]
);
};
<details>
<summary>Examples</summary>
anagrams('abc'); // ['abc','acb','bac','bca','cab','cba']
</details>
<br>β¬ Back to top
byteSize
Returns the length of a string in bytes.
Convert a given string to a Blob
Object and find its size
.
const byteSize = str => new Blob([str]).size;
<details>
<summary>Examples</summary>
byteSize('π'); // 4
byteSize('Hello World'); // 11
</details>
<br>β¬ Back to top
capitalize
Capitalizes the first letter of a string.
Use array destructuring and String.toUpperCase()
to capitalize first letter, ...rest
to get array of characters after first letter and then Array.join('')
to make it a string again.
Omit the lowerRest
parameter to keep the rest of the string intact, or set it to true
to convert to lowercase.
const capitalize = ([first, ...rest], lowerRest = false) =>
first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));
<details>
<summary>Examples</summary>
capitalize('fooBar'); // 'FooBar'
capitalize('fooBar', true); // 'Foobar'
</details>
<br>β¬ Back to top
capitalizeEveryWord
Capitalizes the first letter of every word in a string.
Use String.replace()
to match the first character of each word and String.toUpperCase()
to capitalize it.
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
<details>
<summary>Examples</summary>
capitalizeEveryWord('hello world!'); // 'Hello World!'
</details>
<br>β¬ Back to top
decapitalize
Decapitalizes the first letter of a string.
Use array destructuring and String.toLowerCase()
to decapitalize first letter, ...rest
to get array of characters after first letter and then Array.join('')
to make it a string again.
Omit the upperRest
parameter to keep the rest of the string intact, or set it to true
to convert to uppercase.
const decapitalize = ([first, ...rest], upperRest = false) =>
first.toLowerCase() + (upperRest ? rest.join('').toUpperCase() : rest.join(''));
<details>
<summary>Examples</summary>
decapitalize('FooBar'); // 'fooBar'
decapitalize('FooBar', true); // 'fOOBAR'
</details>
<br>β¬ Back to top
escapeHTML
Escapes a string for use in HTML.
Use String.replace()
with a regexp that matches the characters that need to be escaped, using a callback function to replace each character instance with its associated escaped character using a dictionary (object).
const escapeHTML = str =>
str.replace(
/[&<>'"]/g,
tag =>
({
'&': '&',
'<': '<',
'>': '>',
"'": ''',
'"': '"'
}[tag] || tag)
);
<details>
<summary>Examples</summary>
escapeHTML('<a href="#">Me & you</a>'); // '<a href="#">Me & you</a>'
</details>
<br>β¬ Back to top
escapeRegExp
Escapes a string to use in a regular expression.
Use String.replace()
to escape special characters.
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
<details>
<summary>Examples</summary>
escapeRegExp('(test)'); // \\(test\\)
</details>
<br>β¬ Back to top
fromCamelCase
Converts a string from camelcase.
Use String.replace()
to remove underscores, hyphens, and spaces and convert words to camelcase.
Omit the second argument to use a default separator
of _
.
const fromCamelCase = (str, separator = '_') =>
str
.replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
.replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2')
.toLowerCase();
<details>
<summary>Examples</summary>
fromCamelCase('someDatabaseFieldName', ' '); // 'some database field name'
fromCamelCase('someLabelThatNeedsToBeCamelized', '-'); // 'some-label-that-needs-to-be-camelized'
fromCamelCase('someJavascriptProperty', '_'); // 'some_javascript_property'
</details>
<br>β¬ Back to top
isAbsoluteURL
Returns true
if the given string is an absolute URL, false
otherwise.
Use a regular expression to test if the string is an absolute URL.
const isAbsoluteURL = str => /^[a-z][a-z0-9+.-]*:/.test(str);
<details>
<summary>Examples</summary>
isAbsoluteURL('https://google.com'); // true
isAbsoluteURL('ftp://www.myserver.net'); // true
isAbsoluteURL('/foo/bar'); // false
</details>
<br>β¬ Back to top
isLowerCase
Checks if a string is lower case.
Convert the given string to lower case, using String.toLowerCase()
and compare it to the original.
const isLowerCase = str => str === str.toLowerCase();
<details>
<summary>Examples</summary>
isLowerCase('abc'); // true
isLowerCase('a3@$'); // true
isLowerCase('Ab4'); // false
</details>
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isUpperCase
Checks if a string is upper case.
Convert the given string to upper case, using String.toUpperCase()
and compare it to the original.
const isUpperCase = str => str === str.toUpperCase();
<details>
<summary>Examples</summary>
isUpperCase('ABC'); // true
isLowerCase('A3@$'); // true
isLowerCase('aB4'); // false
</details>
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mask
Replaces all but the last num
of characters with the specified mask character.
Use String.slice()
to grab the portion of the characters that need to be masked and use String.replace()
with a regexp to replace every character with the mask character.
Concatenate the masked characters with the remaining unmasked portion of the string.
Omit the second argument, num
, to keep a default of 4
characters unmasked. If num
is negative, the unmasked characters will be at the start of the string.
Omit the third argument, mask
, to use a default character of '*'
for the mask.
const mask = (cc, num = 4, mask = '*') =>
('' + cc).slice(0, -num).replace(/./g, mask) + ('' + cc).slice(-num);
<details>
<summary>Examples</summary>
mask(1234567890); // '******7890'
mask(1234567890, 3); // '*******890'
mask(1234567890, -4, '$'); // '$$$$567890'
</details>
<br>β¬ Back to top
palindrome
Returns true
if the given string is a palindrome, false
otherwise.
Convert string String.toLowerCase()
and use String.replace()
to remove non-alphanumeric characters from it.
Then, String.split('')
into individual characters, Array.reverse()
, String.join('')
and compare to the original, unreversed string, after converting it String.tolowerCase()
.
const palindrome = str => {
const s = str.toLowerCase().replace(/[\W_]/g, '');
return (
s ===
s
.split('')
.reverse()
.join('')
);
};
<details>
<summary>Examples</summary>
palindrome('taco cat'); // true
</details>
<br>β¬ Back to top
pluralize
Returns the singular or plural form of the word based on the input number. If the first argument is an object
, it will use a closure by returning a function that can auto-pluralize words that don't simply end in s
if the supplied dictionary contains the word.
If num
is either -1
or 1
, return the singular form of the word. If num
is any other number, return the plural form. Omit the third argument to use the default of the singular word + s
, or supply a custom pluralized word when necessary. If the first argument is an object
, utilize a closure by returning a function which can use the supplied dictionary to resolve the correct plural form of the word.
const pluralize = (val, word, plural = word + 's') => {
const _pluralize = (num, word, plural = word + 's') =>
[1, -1].includes(Number(num)) ? word : plural;
if (typeof val === 'object') return (num, word) => _pluralize(num, word, val[word]);
return _pluralize(val, word, plural);
};
<details>
<summary>Examples</summary>
pluralize(0, 'apple'); // 'apples'
pluralize(1, 'apple'); // 'apple'
pluralize(2, 'apple'); // 'apples'
pluralize(2, 'person', 'people'); // 'people'
const PLURALS = {
person: 'people',
radius: 'radii'
};
const autoPluralize = pluralize(PLURALS);
autoPluralize(2, 'person'); // 'people'
</details>
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reverseString
Reverses a string.
Use the spread operator (...
) and Array.reverse()
to reverse the order of the characters in the string.
Combine characters to get a string using String.join('')
.
const reverseString = str => [...str].reverse().join('');
<details>
<summary>Examples</summary>
reverseString('foobar'); // 'raboof'
</details>
<br>β¬ Back to top
sortCharactersInString
Alphabetically sorts the characters in a string.
Use the spread operator (...
), Array.sort()
and String.localeCompare()
to sort the characters in str
, recombine using String.join('')
.
const sortCharactersInString = str => [...str].sort((a, b) => a.localeCompare(b)).join('');
<details>
<summary>Examples</summary>
sortCharactersInString('cabbage'); // 'aabbceg'
</details>
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splitLines
Splits a multiline string into an array of lines.
Use String.split()
and a regular expression to match line breaks and create an array.
const splitLines = str => str.split(/\r?\n/);
<details>
<summary>Examples</summary>
splitLines('This\nis a\nmultiline\nstring.\n'); // ['This', 'is a', 'multiline', 'string.' , '']
</details>
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toCamelCase
Converts a string to camelcase.
Break the string into words and combine them capitalizing the first letter of each word, using a regexp.
const toCamelCase = str => {
let s =
str &&
str
.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.slice(0, 1).toUpperCase() + x.slice(1).toLowerCase())
.join('');
return s.slice(0, 1).toLowerCase() + s.slice(1);
};
<details>
<summary>Examples</summary>
toCamelCase('some_database_field_name'); // 'someDatabaseFieldName'
toCamelCase('Some label that needs to be camelized'); // 'someLabelThatNeedsToBeCamelized'
toCamelCase('some-javascript-property'); // 'someJavascriptProperty'
toCamelCase('some-mixed_string with spaces_underscores-and-hyphens'); // 'someMixedStringWithSpacesUnderscoresAndHyphens'
</details>
<br>β¬ Back to top
toKebabCase
Converts a string to kebab case.
Break the string into words and combine them adding -
as a separator, using a regexp.
const toKebabCase = str =>
str &&
str
.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.toLowerCase())
.join('-');
<details>
<summary>Examples</summary>
toKebabCase('camelCase'); // 'camel-case'
toKebabCase('some text'); // 'some-text'
toKebabCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some-mixed-string-with-spaces-underscores-and-hyphens'
toKebabCase('AllThe-small Things'); // "all-the-small-things"
toKebabCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i-am-listening-to-fm-while-loading-different-url-on-my-browser-and-also-editing-xml-and-html"
</details>
<br>β¬ Back to top
toSnakeCase
Converts a string to snake case.
Break the string into words and combine them adding _
as a separator, using a regexp.
const toSnakeCase = str =>
str &&
str
.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.toLowerCase())
.join('_');
<details>
<summary>Examples</summary>
toSnakeCase('camelCase'); // 'camel_case'
toSnakeCase('some text'); // 'some_text'
toSnakeCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some_mixed_string_with_spaces_underscores_and_hyphens'
toSnakeCase('AllThe-small Things'); // "all_the_smal_things"
toSnakeCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i_am_listening_to_fm_while_loading_different_url_on_my_browser_and_also_editing_some_xml_and_html"
</details>
<br>β¬ Back to top
truncateString
Truncates a string up to a specified length.
Determine if the string's length
is greater than num
.
Return the string truncated to the desired length, with '...'
appended to the end or the original string.
const truncateString = (str, num) =>
str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;
<details>
<summary>Examples</summary>
truncateString('boomerang', 7); // 'boom...'
</details>
<br>β¬ Back to top
unescapeHTML
Unescapes escaped HTML characters.
Use String.replace()
with a regex that matches the characters that need to be unescaped, using a callback function to replace each escaped character instance with its associated unescaped character using a dictionary (object).
const unescapeHTML = str =>
str.replace(
/&|<|>|'|"/g,
tag =>
({
'&': '&',
'<': '<',
'>': '>',
''': "'",
'"': '"'
}[tag] || tag)
);
<details>
<summary>Examples</summary>
unescapeHTML('<a href="#">Me & you</a>'); // '<a href="#">Me & you</a>'
</details>
<br>β¬ Back to top
words
Converts a given string into an array of words.
Use String.split()
with a supplied pattern (defaults to non-alpha as a regexp) to convert to an array of strings. Use Array.filter()
to remove any empty strings.
Omit the second argument to use the default regexp.
const words = (str, pattern = /[^a-zA-Z-]+/) => str.split(pattern).filter(Boolean);
<details>
<summary>Examples</summary>
words('I love javaScript!!'); // ["I", "love", "javaScript"]
words('python, javaScript & coffee'); // ["python", "javaScript", "coffee"]
</details>
<br>β¬ Back to top
π Type
getType
Returns the native type of a value.
Returns lowercased constructor name of value, "undefined"
or "null"
if value is undefined
or null
.
const getType = v =>
v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();
<details>
<summary>Examples</summary>
getType(new Set([1, 2, 3])); // 'set'
</details>
<br>β¬ Back to top
isArray
Checks if the given argument is an array.
Use Array.isArray()
to check if a value is classified as an array.
const isArray = val => Array.isArray(val);
<details>
<summary>Examples</summary>
isArray([1]); // true
</details>
<br>β¬ Back to top
isArrayLike
Checks if the provided argument is array-like (i.e. is iterable).
Use the spread operator (...
) to check if the provided argument is iterable inside a try... catch
block and the comma operator (,
) to return the appropriate value.
const isArrayLike = val => {
try {
return [...val], true;
} catch (e) {
return false;
}
};
<details>
<summary>Examples</summary>
isArrayLike(document.querySelectorAll('.className')); // true
isArrayLike('abc'); // true
isArrayLike(null); // false
</details>
<br>β¬ Back to top
isBoolean
Checks if the given argument is a native boolean element.
Use typeof
to check if a value is classified as a boolean primitive.
const isBoolean = val => typeof val === 'boolean';
<details>
<summary>Examples</summary>
isBoolean(null); // false
isBoolean(false); // true
</details>
<br>β¬ Back to top
isFunction
Checks if the given argument is a function.
Use typeof
to check if a value is classified as a function primitive.
const isFunction = val => typeof val === 'function';
<details>
<summary>Examples</summary>
isFunction('x'); // false
isFunction(x => x); // true
</details>
<br>β¬ Back to top
isNull
Returns true
if the specified value is null
, false
otherwise.
Use the strict equality operator to check if the value and of val
are equal to null
.
const isNull = val => val === null;
<details>
<summary>Examples</summary>
isNull(null); // true
</details>
<br>β¬ Back to top
isNumber
Checks if the given argument is a number.
Use typeof
to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number';
<details>
<summary>Examples</summary>
isNumber('1'); // false
isNumber(1); // true
</details>
<br>β¬ Back to top
isObject
Returns a boolean determining if the passed value is an object or not.
Uses the Object
constructor to create an object wrapper for the given value.
If the value is null
or undefined
, create and return an empty object. Ξtherwise, return an object of a type that corresponds to the given value.
const isObject = obj => obj === Object(obj);
<details>
<summary>Examples</summary>
isObject([1, 2, 3, 4]); // true
isObject([]); // true
isObject(['Hello!']); // true
isObject({ a: 1 }); // true
isObject({}); // true
isObject(true); // false
</details>
<br>β¬ Back to top
isPrimitive
Returns a boolean determining if the passed value is primitive or not.
Use Array.includes()
on an array of type strings which are not primitive,
supplying the type using typeof
.
Since typeof null
evaluates to 'object'
, it needs to be directly compared.
const isPrimitive = val => !['object', 'function'].includes(typeof val) || val === null;
<details>
<summary>Examples</summary>
isPrimitive(null); // true
isPrimitive(50); // true
isPrimitive('Hello!'); // true
isPrimitive(false); // true
isPrimitive(Symbol()); // true
isPrimitive([]); // false
</details>
<br>β¬ Back to top
isPromiseLike
Returns true
if an object looks like a Promise
, false
otherwise.
Check if the object is not null
, its typeof
matches either object
or function
and if it has a .then
property, which is also a function
.
const isPromiseLike = obj =>
obj !== null &&
(typeof obj === 'object' || typeof obj === 'function') &&
typeof obj.then === 'function';
<details>
<summary>Examples</summary>
isPromiseLike({
then: function() {
return '';
}
}); // true
isPromiseLike(null); // false
isPromiseLike({}); // false
</details>
<br>β¬ Back to top
isString
Checks if the given argument is a string.
Use typeof
to check if a value is classified as a string primitive.
const isString = val => typeof val === 'string';
<details>
<summary>Examples</summary>
isString('10'); // true
</details>
<br>β¬ Back to top
isSymbol
Checks if the given argument is a symbol.
Use typeof
to check if a value is classified as a symbol primitive.
const isSymbol = val => typeof val === 'symbol';
<details>
<summary>Examples</summary>
isSymbol(Symbol('x')); // true
</details>
<br>β¬ Back to top
isValidJSON
Checks if the provided argument is a valid JSON.
Use JSON.parse()
and a try... catch
block to check if the provided argument is a valid JSON.
const isValidJSON = obj => {
try {
JSON.parse(obj);
return true;
} catch (e) {
return false;
}
};
<details>
<summary>Examples</summary>
isValidJSON('{"name":"Adam","age":20}'); // true
isValidJSON('{"name":"Adam",age:"20"}'); // false
isValidJSON(null); // true
</details>
<br>β¬ Back to top
π§ Utility
cloneRegExp
Clones a regular expression.
Use new RegExp()
, RegExp.source
and RegExp.flags
to clone the given regular expression.
const cloneRegExp = regExp => new RegExp(regExp.source, regExp.flags);
<details>
<summary>Examples</summary>
const regExp = /lorem ipsum/gi;
const regExp2 = cloneRegExp(regExp); // /lorem ipsum/gi
</details>
<br>β¬ Back to top
coalesce
Returns the first non-null/undefined argument.
Use Array.find()
to return the first non null
/undefined
argument.
const coalesce = (...args) => args.find(_ => ![undefined, null].includes(_));
<details>
<summary>Examples</summary>
coalesce(null, undefined, '', NaN, 'Waldo'); // ""
</details>
<br>β¬ Back to top
coalesceFactory
Returns a customized coalesce function that returns the first argument that returns true
from the provided argument validation function.
Use Array.find()
to return the first argument that returns true
from the provided argument validation function.
const coalesceFactory = valid => (...args) => args.find(valid);
<details>
<summary>Examples</summary>
const customCoalesce = coalesceFactory(_ => ![null, undefined, '', NaN].includes(_));
customCoalesce(undefined, null, NaN, '', 'Waldo'); // "Waldo"
</details>
<br>β¬ Back to top
extendHex
Extends a 3-digit color code to a 6-digit color code.
Use Array.map()
, String.split()
and Array.join()
to join the mapped array for converting a 3-digit RGB notated hexadecimal color-code to the 6-digit form.
Array.slice()
is used to remove #
from string start since it's added once.
const extendHex = shortHex =>
'#' +
shortHex
.slice(shortHex.startsWith('#') ? 1 : 0)
.split('')
.map(x => x + x)
.join('');
<details>
<summary>Examples</summary>
extendHex('#03f'); // '#0033ff'
extendHex('05a'); // '#0055aa'
</details>
<br>β¬ Back to top
getURLParameters
Returns an object containing the parameters of the current URL.
Use String.match()
with an appropriate regular expression to get all key-value pairs, Array.reduce()
to map and combine them into a single object.
Pass location.search
as the argument to apply to the current url
.
const getURLParameters = url =>
url
.match(/([^?=&]+)(=([^&]*))/g)
.reduce((a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a), {});
<details>
<summary>Examples</summary>
getURLParameters('http://url.com/page?name=Adam&surname=Smith'); // {name: 'Adam', surname: 'Smith'}
</details>
<br>β¬ Back to top
hexToRGB
Converts a color code to a rgb()
or rgba()
string if alpha value is provided.
Use bitwise right-shift operator and mask bits with &
(and) operator to convert a hexadecimal color code (with or without prefixed with #
) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba()
string in return.
const hexToRGB = hex => {
let alpha = false,
h = hex.slice(hex.startsWith('#') ? 1 : 0);
if (h.length === 3) h = [...h].map(x => x + x).join('');
else if (h.length === 8) alpha = true;
h = parseInt(h, 16);
return (
'rgb' +
(alpha ? 'a' : '') +
'(' +
(h >>> (alpha ? 24 : 16)) +
', ' +
((h & (alpha ? 0x00ff0000 : 0x00ff00)) >>> (alpha ? 16 : 8)) +
', ' +
((h & (alpha ? 0x0000ff00 : 0x0000ff)) >>> (alpha ? 8 : 0)) +
(alpha ? `, ${h & 0x000000ff}` : '') +
')'
);
};
<details>
<summary>Examples</summary>
hexToRGB('#27ae60ff'); // 'rgba(39, 174, 96, 255)'
hexToRGB('27ae60'); // 'rgb(39, 174, 96)'
hexToRGB('#fff'); // 'rgb(255, 255, 255)'
</details>
<br>β¬ Back to top
httpGet
Makes a GET
request to the passed URL.
Use XMLHttpRequest
web api to make a get
request to the given url
.
Handle the onload
event, by calling the given callback
the responseText
.
Handle the onerror
event, by running the provided err
function.
Omit the third argument, err
, to log errors to the console's error
stream by default.
const httpGet = (url, callback, err = console.error) => {
const request = new XMLHttpRequest();
request.open('GET', url, true);
request.onload = () => callback(request.responseText);
request.onerror = () => err(request);
request.send();
};
<details>
<summary>Examples</summary>
httpGet(
'https://jsonplaceholder.typicode.com/posts/1',
console.log
); /*
Logs: {
"userId": 1,
"id": 1,
"title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
"body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
}
*/
</details>
<br>β¬ Back to top
httpPost
Makes a POST
request to the passed URL.
Use XMLHttpRequest
web api to make a post
request to the given url
.
Set the value of an HTTP
request header with setRequestHeader
method.
Handle the onload
event, by calling the given callback
the responseText
.
Handle the onerror
event, by running the provided err
function.
Omit the third argument, data
, to send no data to the provided url
.
Omit the fourth argument, err
, to log errors to the console's error
stream by default.
const httpPost = (url, callback, data = null, err = console.error) => {
const request = new XMLHttpRequest();
request.open('POST', url, true);
request.setRequestHeader('Content-type', 'application/json; charset=utf-8');
request.onload = () => callback(request.responseText);
request.onerror = () => err(request);
request.send(data);
};
<details>
<summary>Examples</summary>
const newPost = {
userId: 1,
id: 1337,
title: 'Foo',
body: 'bar bar bar'
};
const data = JSON.stringify(newPost);
httpPost(
'https://jsonplaceholder.typicode.com/posts',
console.log,
data
); /*
Logs: {
"userId": 1,
"id": 1337,
"title": "Foo",
"body": "bar bar bar"
}
*/
</details>
<br>β¬ Back to top
parseCookie
Parse an HTTP Cookie header string and return an object of all cookie name-value pairs.
Use String.split(';')
to separate key-value pairs from each other.
Use Array.map()
and String.split('=')
to separate keys from values in each pair.
Use Array.reduce()
and decodeURIComponent()
to create an object with all key-value pairs.
const parseCookie = str =>
str
.split(';')
.map(v => v.split('='))
.reduce((acc, v) => {
acc[decodeURIComponent(v[0].trim())] = decodeURIComponent(v[1].trim());
return acc;
}, {});
<details>
<summary>Examples</summary>
parseCookie('foo=bar; equation=E%3Dmc%5E2'); // { foo: 'bar', equation: 'E=mc^2' }
</details>
<br>β¬ Back to top
prettyBytes
Converts a number in bytes to a human-readable string.
Use an array dictionary of units to be accessed based on the exponent.
Use Number.toPrecision()
to truncate the number to a certain number of digits.
Return the prettified string by building it up, taking into account the supplied options and whether it is negative or not.
Omit the second argument, precision
, to use a default precision of 3
digits.
Omit the third argument, addSpace
, to add space between the number and unit by default.
const prettyBytes = (num, precision = 3, addSpace = true) => {
const UNITS = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
if (Math.abs(num) < 1) return num + (addSpace ? ' ' : '') + UNITS[0];
const exponent = Math.min(Math.floor(Math.log10(num < 0 ? -num : num) / 3), UNITS.length - 1);
const n = Number(((num < 0 ? -num : num) / 1000 ** exponent).toPrecision(precision));
return (num < 0 ? '-' : '') + n + (addSpace ? ' ' : '') + UNITS[exponent];
};
<details>
<summary>Examples</summary>
prettyBytes(1000); // "1 KB"
prettyBytes(-27145424323.5821, 5); // "-27.145 GB"
prettyBytes(123456789, 3, false); // "123MB"
</details>
<br>β¬ Back to top
randomHexColorCode
Generates a random hexadecimal color code.
Use Math.random
to generate a random 24-bit(6x4bits) hexadecimal number. Use bit shifting and then convert it to an hexadecimal String using toString(16)
.
const randomHexColorCode = () => {
let n = ((Math.random() * 0xfffff) | 0).toString(16);
return '#' + (n.length !== 6 ? ((Math.random() * 0xf) | 0).toString(16) + n : n);
};
<details>
<summary>Examples</summary>
randomHexColorCode(); // "#e34155"
</details>
<br>β¬ Back to top
RGBToHex
Converts the values of RGB components to a color code.
Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (<<
) and toString(16)
, then String.padStart(6,'0')
to get a 6-digit hexadecimal value.
const RGBToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
<details>
<summary>Examples</summary>
RGBToHex(255, 165, 1); // 'ffa501'
</details>
<br>β¬ Back to top
serializeCookie
Serialize a cookie name-value pair into a Set-Cookie header string.
Use template literals and encodeURIComponent()
to create the appropriate string.
const serializeCookie = (name, val) => `${encodeURIComponent(name)}=${encodeURIComponent(val)}`;
<details>
<summary>Examples</summary>
serializeCookie('foo', 'bar'); // 'foo=bar'
</details>
<br>β¬ Back to top
timeTaken
Measures the time taken by a function to execute.
Use console.time()
and console.timeEnd()
to measure the difference between the start and end times to determine how long the callback took to execute.
const timeTaken = callback => {
console.time('timeTaken');
const r = callback();
console.timeEnd('timeTaken');
return r;
};
<details>
<summary>Examples</summary>
timeTaken(() => Math.pow(2, 10)); // 1024, (logged): timeTaken: 0.02099609375ms
</details>
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toDecimalMark
Use toLocaleString()
to convert a float-point arithmetic to the Decimal mark form. It makes a comma separated string from a number.
const toDecimalMark = num => num.toLocaleString('en-US');
<details>
<summary>Examples</summary>
toDecimalMark(12305030388.9087); // "12,305,030,388.909"
</details>
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toOrdinalSuffix
Adds an ordinal suffix to a number.
Use the modulo operator (%
) to find values of single and tens digits.
Find which ordinal pattern digits match.
If digit is found in teens pattern, use teens ordinal.
const toOrdinalSuffix = num => {
const int = parseInt(num),
digits = [int % 10, int % 100],
ordinals = ['st', 'nd', 'rd', 'th'],
oPattern = [1, 2, 3, 4],
tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
return oPattern.includes(digits[0]) && !tPattern.includes(digits[1])
? int + ordinals[digits[0] - 1]
: int + ordinals[3];
};
<details>
<summary>Examples</summary>
toOrdinalSuffix('123'); // "123rd"
</details>
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validateNumber
Returns true
if the given value is a number, false
otherwise.
Use !isNaN()
in combination with parseFloat()
to check if the argument is a number.
Use isFinite()
to check if the number is finite.
Use Number()
to check if the coercion holds.
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;
<details>
<summary>Examples</summary>
validateNumber('10'); // true
</details>
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yesNo
Returns true
if the string is y
/yes
or false
if the string is n
/no
.
Use RegExp.test()
to check if the string evaluates to y/yes
or n/no
.
Omit the second argument, def
to set the default answer as no
.
const yesNo = (val, def = false) =>
/^(y|yes)$/i.test(val) ? true : /^(n|no)$/i.test(val) ? false : def;
<details>
<summary>Examples</summary>
yesNo('Y'); // true
yesNo('yes'); // true
yesNo('No'); // false
yesNo('Foo', true); // true
</details>
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