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 — if index < 0, index + array.length is accessed.

The element in the typed array matching the given index. Always returns undefined if index < -array.length or index >= array.length without attempting to access the corresponding property.

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

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); // 18

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); // 11

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

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

• Polyfill of TypedArray.prototype.at in core-js
• JavaScript typed arrays guide
• TypedArray
• TypedArray.prototype.findIndex()
• TypedArray.prototype.indexOf()
• TypedArray.prototype.with()
• Array.prototype.at()
• String.prototype.at()