TypedArray.prototype.at()

BaselineWidely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since March 2022.

Theat() method ofTypedArray instances takes an integer value and returns the item at that index, allowing for positive and negative integers. Negative integers count back from the last item in the typed array. This method has the same algorithm asArray.prototype.at().

Try it

const int8 = new Int8Array([0, 10, -10, 20, -30, 40, -50]);let index = 1;console.log(`An index of ${index} returns the item ${int8.at(index)}`);// Expected output: "An index of 1 returns the item 10"index = -2;console.log(`An index of ${index} returns the item ${int8.at(index)}`);// Expected output: "An index of -2 returns the item 40"

Syntax

at(index)

Parameters

index: Zero-based index of the typed array element to be returned,converted to an integer. Negative index counts back from the end of the typed array — ifindex < 0,index + array.length is accessed.

Return value

The element in the typed array matching the given index. Always returnsundefined ifindex < -array.length orindex >= array.length without attempting to access the corresponding property.

Description

SeeArray.prototype.at() for more details. This method is not generic and can only be called on typed array instances.

Examples

Return the last value of a typed array

The following example provides a function which returns the last element found in a specified array.

const uint8 = new Uint8Array([1, 2, 4, 7, 11, 18]);// A function which returns the last item of a given arrayfunction returnLast(arr) {  return arr.at(-1);}const lastItem = returnLast(uint8);console.log(lastItem); // 18

Comparing methods

Here we compare different ways to select the penultimate (last but one) item of aTypedArray. Whilst all below methods are valid, it highlights the succinctness and readability of theat() method.

// Our typed array with valuesconst uint8 = new Uint8Array([1, 2, 4, 7, 11, 18]);// Using length propertyconst lengthWay = uint8[uint8.length - 2];console.log(lengthWay); // 11// Using slice() method. Note an array is returnedconst sliceWay = uint8.slice(-2, -1);console.log(sliceWay[0]); // 11// Using at() methodconst atWay = uint8.at(-2);console.log(atWay); // 11