JavaScript Array methods

JavaScript provides a rich set of array methods to manipulate and work with arrays. Here is a comprehensive list of these methods along with sample usage:

Mutator Methods
These methods modify the array they are called on.

push()

Adds one or more elements to the end of an array and returns the new length of the array.

sample:

let arr = [1, 2, 3];
arr.push(4);  // arr is now [1, 2, 3, 4]

pop()

Removes the last element from an array and returns that element.

sample:

let arr = [1, 2, 3];
let lastElement = arr.pop();  // arr is now [1, 2]; lastElement is 3

shift()

Removes the first element from an array and returns that element.

sample:

let arr = [1, 2, 3];
let firstElement = arr.shift();  // arr is now [2, 3]; firstElement is 1

unshift()

Adds one or more elements to the beginning of an array and returns the new length of the array.

sample:

let arr = [1, 2, 3];
arr.unshift(0);  // arr is now [0, 1, 2, 3]

splice()

Adds and/or removes elements from an array.

sample:

let arr = [1, 2, 3, 4];
arr.splice(1, 2, 'a', 'b');  // arr is now [1, 'a', 'b', 4]

sort()

Sorts the elements of an array in place and returns the sorted array.

sample:

let arr = [3, 1, 4, 1, 5, 9];
arr.sort();  // arr is now [1, 1, 3, 4, 5, 9]

reverse()

Reverses the order of the elements in an array in place.

sample:

let arr = [1, 2, 3];
arr.reverse();  // arr is now [3, 2, 1]

Accessor Methods

These methods do not modify the array and typically return a new array or a single value.

concat()

Merges two or more arrays.

sample:

let arr1 = [1, 2];
let arr2 = [3, 4];
let newArr = arr1.concat(arr2);  // newArr is [1, 2, 3, 4]

join()

Joins all elements of an array into a string.

sample:

let arr = [1, 2, 3];
let str = arr.join('-');  // str is '1-2-3'

slice()

Returns a shallow copy of a portion of an array into a new array.

sample:

let arr = [1, 2, 3, 4, 5];
let slicedArr = arr.slice(1, 3);  // slicedArr is [2, 3]

indexOf()

Returns the first index at which a given element can be found in the array.

sample:

let arr = [1, 2, 3];
let index = arr.indexOf(2);  // index is 1

lastIndexOf()

Returns the last index at which a given element can be found in the array.

sample:

let arr = [1, 2, 3, 2];
let index = arr.lastIndexOf(2);  // index is 3

includes()

Determines whether an array includes a certain value.

sample:

let arr = [1, 2, 3];
let hasTwo = arr.includes(2);  // hasTwo is true

toString()

Returns a string representing the array.

sample:

let arr = [1, 2, 3];
let str = arr.toString();  // str is '1,2,3'

toLocaleString()

Returns a localized string representing the array.

sample:

let arr = [1, 2, 3];
let str = arr.toLocaleString();  // str might vary based on locale

Iteration Methods

These methods iterate over the array, typically applying a function to each element.

forEach()

Executes a provided function once for each array element.

sample:

let arr = [1, 2, 3];
arr.forEach(element => console.log(element));  // logs 1, 2, 3

map()

Creates a new array with the results of calling a provided function on every element.

sample:

let arr = [1, 2, 3];
let doubled = arr.map(x => x * 2);  // doubled is [2, 4, 6]

filter()

Creates a new array with all elements that pass the test implemented by the provided function.

sample:

let arr = [1, 2, 3, 4];
let evens = arr.filter(x => x % 2 === 0);  // evens is [2, 4]

reduce()

Applies a function against an accumulator and each element to reduce it to a single value.

sample:

let arr = [1, 2, 3, 4];
let sum = arr.reduce((acc, curr) => acc + curr, 0);  // sum is 10

reduceRight()

Applies a function against an accumulator and each element (from right to left) to reduce it to a single value.

sample:

let arr = [1, 2, 3, 4];
let sum = arr.reduceRight((acc, curr) => acc + curr, 0);  // sum is 10

some()

Tests whether at least one element passes the test implemented by the provided function.

sample:

let arr = [1, 2, 3];
let hasEven = arr.some(x => x % 2 === 0);  // hasEven is true

every()

Tests whether all elements pass the test implemented by the provided function.

sample:

let arr = [1, 2, 3];
let allPositive = arr.every(x => x > 0);  // allPositive is true

find()

Returns the first element that satisfies the provided testing function.

sample:

let arr = [1, 2, 3];
let found = arr.find(x => x > 1);  // found is 2

findIndex()

Returns the index of the first element that satisfies the provided testing function.

sample:

let arr = [1, 2, 3];
let index = arr.findIndex(x => x > 1);  // index is 1

flat()

Creates a new array with all sub-array elements concatenated into it recursively up to the specified depth.

sample:

let arr = [1, [2, [3, 4]]];
let flatArr = arr.flat(2);  // flatArr is [1, 2, 3, 4]

flatMap()

First maps each element using a mapping function, then flattens the result into a new array.

sample:

let arr = [1, 2, 3];
let flatMapped = arr.flatMap(x => [x, x * 2]);  // flatMapped is [1, 2, 2, 4, 3, 6]

entries()

Returns a new Array Iterator object that contains the key/value pairs for each index in the array.

sample:

let arr = ['a', 'b', 'c'];
let iterator = arr.entries();
for (let [index, value] of iterator) {
  console.log(index, value);  // logs 0 'a', 1 'b', 2 'c'
}

keys()

Returns a new Array Iterator that contains the keys for each index in the array.

sample:

let arr = ['a', 'b', 'c'];
let iterator = arr.keys();
for (let key of iterator) {
  console.log(key);  // logs 0, 1, 2
}

values()

Returns a new Array Iterator object that contains the values for each index in