TypedArray.prototype.lastIndexOf()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.
The lastIndexOf() method of TypedArray instances returns the last index at which a given element can be found in the typed array, or -1 if it is not present. The typed array is searched backwards, starting at fromIndex. This method has the same algorithm as Array.prototype.lastIndexOf().
Try it
const uint8 = new Uint8Array([10, 20, 50, 50, 50, 60]);
console.log(uint8.lastIndexOf(50, 5));
// Expected output: 4
console.log(uint8.lastIndexOf(50, 3));
// Expected output: 3
Syntax
js
lastIndexOf(searchElement)
lastIndexOf(searchElement, fromIndex)
Parameters
searchElement-
Element to locate in the typed array.
fromIndexOptional-
Zero-based index at which to start searching backwards, converted to an integer.
Return value
The last index of searchElement in the typed array; -1 if not found.
Description
See Array.prototype.lastIndexOf() for more details. This method is not generic and can only be called on typed array instances.
Examples
Using lastIndexOf()
js
const uint8 = new Uint8Array([2, 5, 9, 2]);
uint8.lastIndexOf(2); // 3
uint8.lastIndexOf(7); // -1
uint8.lastIndexOf(2, 3); // 3
uint8.lastIndexOf(2, 2); // 0
uint8.lastIndexOf(2, -2); // 0
uint8.lastIndexOf(2, -1); // 3
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-%typedarray%.prototype.lastindexof |