JavaScript Array Methods

JavaScript Array length

The length property returns the length (size) of an array:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let size = fruits.length;

JavaScript Array toString()

The JavaScript method toString() converts an array to a string of (comma separated) array values.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();

JavaScript Array at()

ES2022 intoduced the array method at():

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.at(2);

Get the third element of fruits using []:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits[2];

The at() method returns an indexed element from an array.

The at() method returns the same as [].

The at() method is supported in all modern browsers since March 2022:

JavaScript Array join()

The join() method also joins all array elements into a string.

It behaves just like toString(), but in addition you can specify the separator:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.join(" * ");

Popping and Pushing

When you work with arrays, it is easy to remove elements and add new elements.

This is what popping and pushing is:

Popping items out of an array, or pushing items into an array.

JavaScript Array pop()

The pop() method removes the last element from an array:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();

The pop() method returns the value that was “popped out”:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.pop();

JavaScript Array push()

The push() method adds a new element to an array (at the end):

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");

The push() method returns the new array length:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let length = fruits.push("Kiwi");

Shifting Elements

Shifting is equivalent to popping, but working on the first element instead of the last.

JavaScript Array shift()

The shift() method removes the first array element and “shifts” all other elements to a lower index.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift();

The shift() method returns the value that was “shifted out”:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.shift();

JavaScript Array unshift()

The unshift() method adds a new element to an array (at the beginning), and “unshifts” older elements:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");

The unshift() method returns the new array length:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");

Changing Elements

Array elements are accessed using their index number:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[0] = "Kiwi";

JavaScript Array length

The length property provides an easy way to append a new element to an array:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[fruits.length] = "Kiwi";

JavaScript Array delete()

const fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0];

Merging Arrays (Concatenating)

In programming languages, concatenation means joining strings end-to-end.

Concatenation “snow” and “ball” gives “snowball”.

Concatenating arrays means joining arrays end-to-end.

JavaScript Array concat()

The concat() method creates a new array by merging (concatenating) existing arrays:

const myGirls = ["Cecilie", "Lone"];
const myBoys = ["Emil", "Tobias", "Linus"];

const myChildren = myGirls.concat(myBoys);

const arr1 = ["Cecilie", "Lone"];
const arr2 = ["Emil", "Tobias", "Linus"];
const arr3 = ["Robin", "Morgan"];
const myChildren = arr1.concat(arr2, arr3);

The concat() method can also take strings as arguments :

const arr1 = ["Emil", "Tobias", "Linus"];
const myChildren = arr1.concat("Peter");

Array copyWithin()

The copyWithin() method copies array elements to another position in an array:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.copyWithin(2, 0);

Copy to index 2, the elements from index 0 to 2:

const fruits = ["Banana", "Orange", "Apple", "Mango", "Kiwi"];
fruits.copyWithin(2, 0, 2);

Flattening an Array

Flattening an array is the process of reducing the dimensionality of an array.

Flattening is useful when you want to convert a multi-dimensional array into a one-dimensional array.

JavaScript Array flat()

ES2019 Introduced the Array flat() method.

The flat() method creates a new array with sub-array elements concatenated to a specified depth.

const myArr = [[1,2],[3,4],[5,6]];
const newArr = myArr.flat();

Browser Support

JavaScript Array flat() is supported in all modern browsers since January 2020:

JavaScript Array flatMap()

ES2019 added the Array flatMap() method to JavaScript.

The flatMap() method first maps all elements of an array and then creates a new array by flattening the array.

const myArr = [1, 2, 3, 4, 5, 6];
const newArr = myArr.flatMap(x => [x, x * 10]);

Browser Support

JavaScript Array flatMap() is supported in all modern browsers since January 2020:

Splicing and Slicing Arrays

The splice() method adds new items to an array.

The slice() method slices out a piece of an array.

JavaScript Array splice()

The splice() method can be used to add new items to an array:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 0, "Lemon", "Kiwi");

The first parameter (2) defines the position where new elements should be added (spliced in).

The second parameter (0) defines how many elements should be removed.

The rest of the parameters (“Lemon” , “Kiwi”) define the new elements to be added.

The splice() method returns an array with the deleted items:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 2, "Lemon", "Kiwi");

Using splice() to Remove Elements

With clever parameter setting, you can use splice() to remove elements without leaving “holes” in the array:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(0, 1);

The first parameter (0) defines the position where new elements should be added (spliced in).

The second parameter (1) defines how many elements should be removed.

The rest of the parameters are omitted. No new elements will be added.

JavaScript Array toSpliced()

ES2023 added the Array toSpliced() method as a safe way to splice an array without altering the original array.

The difference between the new toSpliced() method and the old splice() method is that the new method creates a new array, keeping the original array unchanged, while the old method altered the original array.

const months = ["Jan", "Feb", "Mar", "Apr"];
const spliced = months.toSpliced(0, 1);

JavaScript Array slice()

The slice() method slices out a piece of an array into a new array:

const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1);

const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(3);

The slice() method can take two arguments like slice(1, 3).

The method then selects elements from the start argument, and up to (but not including) the end argument.

const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1, 3);

If the end argument is omitted, like in the first examples, the slice() method slices out the rest of the array.

const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(2);

Automatic toString()

JavaScript automatically converts an array to a comma separated string when a primitive value is expected.

This is always the case when you try to output an array.

These two examples will produce the same result:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits;