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();…


This content originally appeared on DEV Community and was authored by Muhammad Usman

Mutator Methods (Modify the original array)

  1. push(element1, ..., elementN) Adds elements to the end. Returns: New length. 
arr.push(5); // [1,2,3] → [1,2,3,5]
  1. pop() Removes the last element. Returns: Removed element.

arr.pop(); // [1,2,3] → [1,2]

  1. shift() Removes the first element. Returns: Removed element. 
arr.shift(); // [1,2,3] → [2,3]
  1. unshift(element1, ..., elementN) Adds elements to the start. Returns: New length. 
arr.unshift(0); // [1,2,3] → [0,1,2,3]
  1. 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]
  1. sort([compareFunction]) Sorts elements (lexicographically by default). Returns: Sorted array (mutates original). 
arr.sort((a, b) => a - b); // [3,1,2] → [1,2,3]
  1. reverse() Reverses the array. Returns: Reversed array (mutates original). 
arr.reverse(); // [1,2,3] → [3,2,1]
  1. fill(value, start?, end?) Fills array with value between start and end. 
arr.fill(0); // [1,2,3] → [0,0,0]
  1. 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)

  1. concat(...arrays) Merges arrays. Returns: New merged array. 
arr.concat([4,5]); // [1,2,3] → [1,2,3,4,5]
  1. slice(start?, end?) Returns subarray between start and end. 
arr.slice(1, 3); // [1,2,3,4] → [2,3]
  1. join(separator?) Joins elements into a string (default: ,). 
arr.join('-'); // [1,2,3] → "1-2-3"
  1. includes(element) Checks if array contains element. Returns: true/false. 
arr.includes(2); // [1,2,3] → true
  1. indexOf(element) Returns first index of element or -1. 
arr.indexOf(2); // [1,2,3] → 1
  1. lastIndexOf(element) Returns last index of element or -1. 
[1,2,2,3].lastIndexOf(2); // → 2
  1. toString() Same as join(). 
[1,2,3].toString(); // "1,2,3"
  1. toSorted() (ES2023) Non-mutating version of sort(). 
const sorted = arr.toSorted();
  1. toReversed() (ES2023) Non-mutating version of reverse(). 
const reversed = arr.toReversed();

Iteration Methods

  1. forEach(callback) Executes callback for each element. Returns: undefined. 
arr.forEach(x => console.log(x));
  1. map(callback) Returns new array with transformed elements. 
const doubled = arr.map(x => x * 2);
  1. filter(callback) Returns elements that pass callback test. 
const evens = arr.filter(x => x % 2 === 0);
  1. reduce(callback, initialValue?) Reduces array to a single value. 
const sum = arr.reduce((acc, x) => acc + x, 0);
  1. find(callback) Returns first element passing callback test. 
const firstEven = arr.find(x => x % 2 === 0);
  1. some(callback) Checks if at least one element passes test. Returns: true/false. 
const hasEven = arr.some(x => x % 2 === 0);
  1. every(callback) Checks if all elements pass test. 
const allEven = arr.every(x => x % 2 === 0);
  1. flat(depth = 1) Flattens nested arrays. 
[1, [2]].flat(); // → [1,2]
  1. flatMap(callback) Maps then flattens the result. 
arr.flatMap(x => [x, x*2]); // [1,2] → [1,2,2,4]

Static Methods

  1. Array.isArray(value) Checks if value is an array. 
Array.isArray([1,2]); // → true
  1. Array.from(arrayLike) Creates an array from array-like/iterable. 
Array.from('123'); // → ['1','2','3']
  1. Array.of(...elements) Creates an array from arguments. 
Array.of(1,2,3); // → [1,2,3]

ES6+ Additions

  1. at(index) Returns element at index (supports negatives). 
[1,2,3].at(-1); // → 3
  1. 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+).


This content originally appeared on DEV Community and was authored by Muhammad Usman


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