The lastIndexOf() method 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(). TypedArray is one of the typed array types here.


<var>typedarray</var>.<var><code>lastIndexOf(<var>searchElement</var>[, <var>fromIndex</var> = typedarray.length])</code></var>


Element to locate in the typed array.
Optional. The index at which to start searching backwards. Defaults to the typed array's length, i.e. the whole typed array will be searched. If the index is greater than or equal to the length of the typed array, the whole typed array will be searched. If negative, it is taken as the offset from the end of the typed array. Note that even when the index is negative, the typed array is still searched from back to front. If the calculated index is less than 0, -1 is returned, i.e. the typed array will not be searched.

Return value

The last index of the element in the array; -1 if not found.


lastIndexOf compares searchElement to elements of the typed array using strict equality (the same method used by the ===, or triple-equals, operator).


var 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


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'TypedArray.prototype.lastIndexOf' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'TypedArray.prototype.lastIndexOf' in that specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support No support 37 (37) No support No support No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 37 (37) No support No support No support

Compatibility notes

  • Starting with Firefox 47 (Firefox 47 / Thunderbird 47 / SeaMonkey 2.44),  this method will no longer return -0.
    For example, new Uint8Array([0]).lastIndexOf(0, -0) will now always return +0 (bug 1242043).

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

ECMAScript6 JavaScript Method Prototype TypedArray TypedArrays