Array.prototype.at()

Summary: in this tutorial, you will learn how to use the JavaScript Array at() method to return an element by an index.

Introduction to the JavaScript Array at() method

In JavaScript, you can use the square bracket [] to access an element of an array. For example, the arr[0] returns the first element in the array arr, the arr[1] returns the second element, and so on.

To get the last element in an array, you use the length property like this:

arr[length-1]Code language: CSS (css)

JavaScript doesn’t allow you to use a negative index to access the last element like other languages like Python.

For example, the following returns undefined in JavaScript.

arr[-1]Code language: CSS (css)

The reason is that JavaScript also uses square brackets [] for accessing a property of an object.

For example, the obj[1] returns a property of the object obj with the key "1". Hence, the obj[-1] returns the property of an object with the key "-1".

In the above example, the arr[-1] returns the property of the arr object with the key "-1".

Note that the type of an array is object. Since the "-1" property doesn’t exist in the arr object, it returns undefined.

For this reason, ES2022 introduced a new method at() added to the prototype of Array, String, and TypeArray. This tutorial focuses on the at() method of the Array.prototype.

The at() method accepts an index and returns an element at that index. Here’s the syntax of the at() method:

at(index)

In this syntax, the index specifies an array element to return. It can be zero, positive, or negative.

If the index is zero or positive, the at() method works like the [].

However, if you use a negative index, the method returns an element from the end of the array. For example, the arr.at(-1) returns the last element, arr.at(-2) returns the second last element, and so on.

JavaScript Array at() method example

The following example shows how to use the at() method to return an array element:

const scores = [5, 6, 7];

console.log(scores.at(1)); // same as scores[1] 

// get the last element
console.log(scores.at(-1)); // 7

console.log(scores.at(-1) === scores[scores.length - 1]); // trueCode language: JavaScript (javascript)

Output:

6
7
trueCode language: JavaScript (javascript)

Summary

• Use the at() method to return an element of an array by an index.
• The at() method with a negative index will return an element from the end of the array.