Awesome
eslint-plugin-array-func
Rules for Array functions and methods.
Contents
Installation
Install ESLint either locally or globally.
$ npm install -D eslint
If you installed ESLint
globally, you have to install the array-func
plugin globally too. Otherwise, install it locally.
$ npm install -D eslint-plugin-array-func
Rules
from-map
Prefer using the mapFn
callback of Array.from
over an immediate .map()
call on the Array.from
result.
Array.from
has a mapFn
callback that lets you map the items of the iterable to an array like you would with .map()
except that values have not yet been truncated to fit types allowed in an array. Some iterables can't be directly converted to an array and thus have to be iterated either way. In that case using the mapping callback of Array.from
avoids an iteration. See also MDN for an explanation of the potential benefits of using the mapping callback of Array.from
directly.
This rule is auto fixable. It will produce nested function calls if you use the Array.from
map callback and have a .map()
call following it.
Examples
Code that triggers this rule:
Array.from(iterable).map((t) => t.id);
Array.from(iterable, (t) => t.id).map((id) => id[0]);
Code that doesn't trigger this rule:
Array.from(iterable, (t) => t.id);
Array.from(iterable, function(t) { this.format(t); }, this);
const arr = Array.from(iterable);
const mappedArray = arr.map((t) => t.id);
Using the rule
To use this rule, your eslint.config.js
should at least contain the following:
import arrayFunc from "eslint-plugin-array-func";
export default [
{
plugins: {
"array-func": arrayFunc
},
rules: {
"array-func/from-map": "error"
}
}
];
Alternatively you can use a configuration included with this plugin.
no-unnecessary-this-arg
Avoid the this
parameter when providing arrow function as callback in array functions.
The this
parameter is useless when providing arrow functions, since the this
of arrow functions can not be rebound, thus the parameter has no effect.
The fix is usually to omit the parameter. The Array methods can't be auto-fixed, since the detection of array methods is not confident enough to know that the method is being called on an array.
Checked Functions
from
(fixable)
Checked Methods
every
filter
find
findIndex
forEach
map
some
Examples
Code that triggers this rule:
const array = Array.from("example", (char) => char.charCodeAt(0), this);
const e = array.find((char) => char === 101, this);
const exampleAsArray = array.map((char) => String.fromCharCode(char), this);
const eIndex = array.findIndex((char) => char === 101, this);
const containsE = array.some((char) => char === 101, this);
const isOnlyE = array.every((char) => char === 101, this);
const onlyEs = array.filter((char) => char === 101, this);
array.forEach((char) => console.log(char), this);
Code that doesn't trigger this rule:
const array = Array.from("example", (char) => char.charCodeAt(0));
const alternateArray = Array.from("example", function(char) {
return char.charCodeAt(this)
}, 0);
const e = array.find((char) => char === 101);
const exampleAsArray = array.map((char) => String.fromCharCode(char));
const eIndex = array.findIndex((char) => char === 101);
const containsE = array.some((char) => char === 101);
const isOnlyE = array.every((char) => char === 101);
const onlyEs = array.filter(function(char) {
return char === this
}, 101);
array.forEach(function(char) {
this.log(char);
}, console);
array.filter(this.isGood, this);
Using the rule
To use this rule, your eslint.config.js
should at least contain the following:
import arrayFunc from "eslint-plugin-array-func";
export default [
{
plugins: {
"array-func": arrayFunc
},
rules: {
"array-func/no-unnecessary-this-arg": "error"
}
}
];
Alternatively you can use a configuration included with this plugin.
prefer-array-from
Use Array.from
instead of [...iterable]
.
See from-map
for additional benefits Array.from
can provide over the spread syntax.
This rule is auto fixable.
Examples
Code that triggers this rule:
const iterable = [..."string"];
const arrayCopy = [...iterable];
Code that doesn't trigger this rule:
const array = [1, 2, 3];
const extendedArray = [0, ...array];
const arrayCopy = Array.from(array);
const characterArray = Array.from("string");
Using the rule
To use this rule, your eslint.config.js
should at least contain the following:
import arrayFunc from "eslint-plugin-array-func";
export default [
{
plugins: {
"array-func": arrayFunc
},
rules: {
"array-func/prefer-array-from": "error"
}
}
];
Alternatively you can use a configuration included with this plugin.
avoid-reverse
Avoid reversing the array and running a method on it if there is an equivalent of the method operating on the array from the other end.
There are two operations with such equivalents: reduce
with reduceRight
.
This rule is auto fixable.
Examples
Code that triggers this rule:
const string = array.reverse().reduce((p, c) => p + c, '');
const reverseString = array.reverse().reduceRight((p, c) => p + c, '');
Code that doesn't trigger this rule:
const reverseString = array.reduce((p, c) => p + c, '');
const string = array.reduceRight((p, c) => p + c, '');
const reverseArray = array.reverse();
const reverseMap = array.reverse().map((r) => r + 1);
Using the rule
To use this rule, your eslint.config.js
should at least contain the following:
import arrayFunc from "eslint-plugin-array-func";
export default [
{
plugins: {
"array-func": arrayFunc
},
rules: {
"array-func/avoid-reverse": "error"
}
}
];
Alternatively you can use a configuration included with this plugin.
prefer-flat-map
Use .flatMap()
to map and then flatten an array instead of using .map().flat()
.
This rule is auto fixable.
Examples
Code that triggers this rule:
const mappedAndFlattened = array.map((p) => p).flat();
const flatWithDefaultDepth = array.map((r) => r).flat(1);
Code that doesn't trigger this rule:
const oneAction = array.flatMap((m) => m);
const flattened = array.flat();
const mapped = array.map((r) => r + 1);
const flattenedThenMapped = array.flat().map((r) => r + 1);
const flatMappedWithExtra = array.map((r) => r + 1).reverse().flat();
const flatWithDepth = array.map((p) => p).flat(99);
Using the rule
To use this rule, your eslint.config.js
should at least contain the following:
import arrayFunc from "eslint-plugin-array-func";
export default [
{
plugins: {
"array-func": arrayFunc
},
rules: {
"array-func/prefer-flat-map": "error"
}
}
];
Alternatively you can use a configuration included with this plugin.
prefer-flat
Use .flat()
to flatten an array of arrays. This rule currently recognizes two
patterns and can replace them with a .flat()
call:
[].concat(...array)
array.reduce((p, n) => p.concat(n), [])
This rule is auto fixable.
Examples
Code that triggers this rule:
const concatFlat = [].concat(...array);
const reduceFlat = array.reduce((p, n) => p.concat(n), []);
Code that doesn't trigger this rule:
const flattened = array.flat();
const reverseFlat = array.reduce((p, n) => n.concat(p), []);
const otherReduce = array.reduce((p, n) => n + p, 0);
Using the rule
To use this rule, your eslint.config.js
should at least contain the following:
import arrayFunc from "eslint-plugin-array-func";
export default [
{
plugins: {
"array-func": arrayFunc
},
rules: {
"array-func/prefer-flat": "error"
}
}
];
Alternatively you can use a configuration included with this plugin.
Configurations
recommended
Configuration
Rule | Error level | Fixable |
---|---|---|
array-func/from-map | Error | Yes |
array-func/no-unnecessary-this-arg | Error | Sometimes |
array-func/prefer-array-from | Error | Yes |
array-func/avoid-reverse | Error | Yes |
Using the Configuration
To enable this configuration, import the plugin and add the config to your eslint config array:
import arrayFunc from "eslint-plugin-array-func";
export default [
arrayFunc.configs.recommended,
];
all
Configuration
The recommended configuration does not include all rules, since some Array methods were added after ES2015. The all configuration enables all rules the plugin containsy.
Rule | Error level | Fixable |
---|---|---|
array-func/from-map | Error | Yes |
array-func/no-unnecessary-this-arg | Error | Sometimes |
array-func/prefer-array-from | Error | Yes |
array-func/avoid-reverse | Error | Yes |
array-func/prefer-flat-map | Error | Yes |
array-func/prefer-flat | Error | Yes |
Using the Configuration
To enable this configuration, import the plugin and add the config to your eslint config array:
import arrayFunc from "eslint-plugin-array-func";
export default [
arrayFunc.configs.all,
];
License
The array-func
plugin is licensed under the MIT License.