TypedArray.prototype.at()

The at() method 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 array.

This is not to suggest there is anything wrong with using the square bracket notation. For example array[0] would return the first item. However instead of using array.length for latter items; e.g. array[array.length-1] for the last item, you can call array.at(-1). (See the examples below)

Syntax

at(index)

Parameters

index
The index (position) of the array element to be returned. Supports relative indexing from the end of the array when passed a negative index. i.e. If a negative number is used the element returned will be found by counting back from the end of the array.

Return value

The element in the array matching the given index. Returns undefined if the given index can not be found.

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 array
function returnLast(arr) {
  return arr.at(-1);
}

const lastItem = returnLast(uint8);
console.log(lastItem); // Logs: 18

Comparing methods

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

// Our typed array with values
const uint8 = new Uint8Array([1, 2, 4, 7, 11, 18]);

// Using length property
const lengthWay = uint8[uint8.length-2];
console.log(lengthWay); // Logs: 11

// Using slice() method. Note an array is returned
const sliceWay = uint8.slice(-2, -1);
console.log(sliceWay[0]); // Logs: 11

// Using at() method
const atWay = uint8.at(-2);
console.log(atWay); // Logs: 11

Specifications

Specification
Relative Indexing Method
# sec-%typedarray.prototype%-additions

Browser compatibility

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See also