JS Array Methods

Basic Array Methods

Col 1	Col 2
Array length Array toString() Array at() Array join() Array pop() Array push() Array shift() Array unshift()	Array isArray() Array delete() Array concat() Array copyWithin() Array flat() Array slice() Array splice() Array toSpliced()

Complete JavaScript Array Reference

JavaScript Array length

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

Example

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

let size = fruits.length;

The length property can also be used to set the length of an array:

Example

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

fruits.length = 2;

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JavaScript Array toString()

The toString() method returns the elements of an array as a comma separated string.

Example

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

let myList = fruits.toString();

Note: Every JavaScript object has a toString() method. The toString() method is used internally by JavaScript when an object needs to be displayed as a text (like in HTML), or when an object needs to be used as a string.

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JavaScript Array at()

ES2022 introduced the array method at():

Examples

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

let fruit = fruits.at(2);

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

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

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Browser Support

at() is an ECMAScript 2022 feature.

JavaScript 2022 is supported in all modern browsers since March 2022:

Note: Many languages allow negative bracket indexing like [-1] to access elements from the end of an object / array / string. This is not possible in JavaScript, because [] is used for accessing both arrays and objects. obj[-1] refers to the value of key -1, not to the last property of the object. The at() method was introduced in ES2022 to solve this problem.

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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:

Example

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

document.getElementById("demo").innerHTML = fruits.join(" * ");

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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.

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JavaScript Array pop()

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

Example

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

fruits.pop();

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

Example

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

let fruit = fruits.pop();

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JavaScript Array push()

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

Example

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

fruits.push("Kiwi");

The push() method returns the new array length:

Example

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

let length = fruits.push("Kiwi");

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Shifting Elements

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

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JavaScript Array shift()

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

Example

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

fruits.shift();

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

Example

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

let fruit = fruits.shift();

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JavaScript Array unshift()

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

Example

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

fruits.unshift("Lemon");

The unshift() method returns the new array length:

Example

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

fruits.unshift("Lemon");

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Changing Elements

Array elements are accessed using their index number:

Note: Array indexes start with 0: [0] is the first array element [1] is the second [2] is the third ...

Example

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

fruits[0] = "Kiwi";

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JavaScript Array length

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

Example

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

fruits[fruits.length] = "Kiwi";

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Array.isArray()

ECMAScript 5 (JavaScript 2009) added the new method Array.isArray() to JavaScript:

Example

Array.isArray(fruits);

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JavaScript Array delete()

Warning: ! Using delete() leaves undefined holes in the array. Use pop() or shift() instead.

Example

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

delete fruits[0];

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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.

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JavaScript Array concat()

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

Example (Merging Two Arrays)

const myGirls = ["Cecilie", "Lone"];

const myBoys = ["Emil", "Tobias", "Linus"];

const myChildren = myGirls.concat(myBoys);

Note: The concat() method does not change the existing arrays. It always returns a new array. The concat() method can take any number of array arguments.

Example (Merging Three Arrays)

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:

Example (Merging an Array with Values)

const arr1 = ["Emil", "Tobias", "Linus"];

const myChildren = arr1.concat("Peter");

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Array copyWithin()

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

Examples

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

fruits.copyWithin(2, 0);

Note: The copyWithin() method overwrites the existing values. The copyWithin() method does not add items to the array. The copyWithin() method does not change the length of the array.

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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.

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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.

Example

const myArr = [[1,2],[3,4],[5,6]];

const newArr = myArr.flat();

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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.

Example

const myArr = [1, 2, 3, 4, 5, 6];

const newArr = myArr.flatMap(x => [x, x * 10]);

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Splicing and Slicing Arrays

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

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

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JavaScript Array splice()

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

Example

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:

Example

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

fruits.splice(2, 2, "Lemon", "Kiwi");

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Using splice() to Remove Elements

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

Example

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.

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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.

Example

const months = ["Jan", "Feb", "Mar", "Apr"];

const spliced = months.toSpliced(0, 1);

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JavaScript Array slice()

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

Example

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

const citrus = fruits.slice(1);

Note: The slice() method creates a new array. The slice() method does not remove any elements from the source array.

Example

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.

Example

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.

Example

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

const citrus = fruits.slice(2);

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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:

Example

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

document.getElementById("demo").innerHTML = fruits.toString();

Example

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

document.getElementById("demo").innerHTML = fruits;

Note: All JavaScript objects have a toString() method.

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Searching Arrays

Searching arrays are covered in the next chapter of this tutorial.

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Sorting Arrays

Sorting arrays covers the methods used to sort arrays.

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Iterating Arrays

Iterating arrays covers methods that operate on all array elements.