JavaScript Array Methods Cheat Sheet: The Only Guide You Need

Mutator Methods (Modify the original array) push(element1, ..., elementN) Adds elements to the end. Returns: New length. arr.push(5); // [1,2,3] → [1,2,3,5] pop() Removes the last element. Returns: Removed element. arr.pop(); // [1,2,3] → [1,2] shift() Removes the first element. Returns: Removed element. arr.shift(); // [1,2,3] → [2,3] unshift(element1, ..., elementN) Adds elements to the start. Returns: New length. arr.unshift(0); // [1,2,3] → [0,1,2,3] splice(start, deleteCount, ...items) Adds/removes elements at start index. Returns: Array of removed elements. arr.splice(1, 1, 'a'); // [1,2,3] → [1,'a',3] sort([compareFunction]) Sorts elements (lexicographically by default). Returns: Sorted array (mutates original). arr.sort((a, b) => a - b); // [3,1,2] → [1,2,3] reverse() Reverses the array. Returns: Reversed array (mutates original). arr.reverse(); // [1,2,3] → [3,2,1] fill(value, start?, end?) Fills array with value between start and end. arr.fill(0); // [1,2,3] → [0,0,0] copyWithin(target, start, end?) Copies elements within the array. [1,2,3,4].copyWithin(0, 2); // → [3,4,3,4] Accessor Methods (Return new data without modifying the array) concat(...arrays) Merges arrays. Returns: New merged array. arr.concat([4,5]); // [1,2,3] → [1,2,3,4,5] slice(start?, end?) Returns subarray between start and end. arr.slice(1, 3); // [1,2,3,4] → [2,3] join(separator?) Joins elements into a string (default: ,). arr.join('-'); // [1,2,3] → "1-2-3" includes(element) Checks if array contains element. Returns: true/false. arr.includes(2); // [1,2,3] → true indexOf(element) Returns first index of element or -1. arr.indexOf(2); // [1,2,3] → 1 lastIndexOf(element) Returns last index of element or -1. [1,2,2,3].lastIndexOf(2); // → 2 toString() Same as join(). [1,2,3].toString(); // "1,2,3" toSorted() (ES2023) Non-mutating version of sort(). const sorted = arr.toSorted(); toReversed() (ES2023) Non-mutating version of reverse(). const reversed = arr.toReversed(); Iteration Methods forEach(callback) Executes callback for each element. Returns: undefined. arr.forEach(x => console.log(x)); map(callback) Returns new array with transformed elements. const doubled = arr.map(x => x * 2); filter(callback) Returns elements that pass callback test. const evens = arr.filter(x => x % 2 === 0); reduce(callback, initialValue?) Reduces array to a single value. const sum = arr.reduce((acc, x) => acc + x, 0); find(callback) Returns first element passing callback test. const firstEven = arr.find(x => x % 2 === 0); some(callback) Checks if at least one element passes test. Returns: true/false. const hasEven = arr.some(x => x % 2 === 0); every(callback) Checks if all elements pass test. const allEven = arr.every(x => x % 2 === 0); flat(depth = 1) Flattens nested arrays. [1, [2]].flat(); // → [1,2] flatMap(callback) Maps then flattens the result. arr.flatMap(x => [x, x*2]); // [1,2] → [1,2,2,4] Static Methods Array.isArray(value) Checks if value is an array. Array.isArray([1,2]); // → true Array.from(arrayLike) Creates an array from array-like/iterable. Array.from('123'); // → ['1','2','3'] Array.of(...elements) Creates an array from arguments. Array.of(1,2,3); // → [1,2,3] ES6+ Additions at(index) Returns element at index (supports negatives). [1,2,3].at(-1); // → 3 findLast(callback) (ES2023) Returns last element passing test. [1,2,2,3].findLast(x => x === 2); // → 2 Key Notes: Mutators: Modify the original array (e.g., push, sort). Accessors: Return new data without changing the original (e.g., slice, concat). Iterators: Process elements via callbacks (e.g., map, filter). Use toSorted(), toReversed(), etc., for non-mutating operations (ES2023+).

Feb 6, 2025 - 07:13

arr.push(5); // [1,2,3] → [1,2,3,5]

arr.pop(); // [1,2,3] → [1,2]

arr.shift(); // [1,2,3] → [2,3]

unshift(element1, ..., elementN) Adds elements to the start. Returns: New length.

arr.unshift(0); // [1,2,3] → [0,1,2,3]

splice(start, deleteCount, ...items) Adds/removes elements at start index. Returns: Array of removed elements.

arr.splice(1, 1, 'a'); // [1,2,3] → [1,'a',3]

sort([compareFunction]) Sorts elements (lexicographically by default). Returns: Sorted array (mutates original).

arr.sort((a, b) => a - b); // [3,1,2] → [1,2,3]

arr.reverse(); // [1,2,3] → [3,2,1]

arr.fill(0); // [1,2,3] → [0,0,0]

[1,2,3,4].copyWithin(0, 2); // → [3,4,3,4]

arr.concat([4,5]); // [1,2,3] → [1,2,3,4,5]

arr.slice(1, 3); // [1,2,3,4] → [2,3]

arr.join('-'); // [1,2,3] → "1-2-3"

includes(element) Checks if array contains element. Returns: true/false.

arr.includes(2); // [1,2,3] → true

arr.indexOf(2); // [1,2,3] → 1

[1,2,2,3].lastIndexOf(2); // → 2

[1,2,3].toString(); // "1,2,3"

const sorted = arr.toSorted();

const reversed = arr.toReversed();

arr.forEach(x => console.log(x));

const doubled = arr.map(x => x * 2);

const evens = arr.filter(x => x % 2 === 0);

const sum = arr.reduce((acc, x) => acc + x, 0);

const firstEven = arr.find(x => x % 2 === 0);

some(callback) Checks if at least one element passes test. Returns: true/false.

const hasEven = arr.some(x => x % 2 === 0);

const allEven = arr.every(x => x % 2 === 0);

[1, [2]].flat(); // → [1,2]

arr.flatMap(x => [x, x*2]); // [1,2] → [1,2,2,4]

Array.isArray([1,2]); // → true

Array.from('123'); // → ['1','2','3']

Array.of(1,2,3); // → [1,2,3]

[1,2,3].at(-1); // → 3

[1,2,2,3].findLast(x => x === 2); // → 2

Mutators: Modify the original array (e.g., push, sort).
Accessors: Return new data without changing the original (e.g., slice, concat).
Iterators: Process elements via callbacks (e.g., map, filter).
Use toSorted(), toReversed(), etc., for non-mutating operations (ES2023+).