The findIndex()
method returns an index in the typed array, if an element in the typed array satisfies the provided testing function. Otherwise -1 is returned.
See also the find()
method, which returns the value of a found element in the typed array instead of its index.
Syntax
typedarray.findIndex(callback[, thisArg])
Parameters
callback
- Function to execute on each value in the typed array, taking three arguments:
element
- The current element being processed in the typed array.
index
- The index of the current element being processed in the typed array.
array
- The typed array
findIndex
was called upon.
thisArg
- Optional. Object to use as
this
when executingcallback
.
Return value
An index in the array if an element passes the test; otherwise, -1.
Description
The findIndex
method executes the callback
function once for each element present in the typed array until it finds one where callback
returns a true value. If such an element is found, findIndex
immediately returns the index of that element. Otherwise, findIndex
returns -1. callback
is invoked only for indexes of the typed array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values.
callback
is invoked with three arguments: the value of the element, the index of the element, and the typed array object being traversed.
If a thisArg
parameter is provided to findIndex
, it will be used as the this
for each invocation of the callback
. If it is not provided, then undefined
is used.
findIndex
does not mutate the typed array on which it is called.
The range of elements processed by findIndex
is set before the first invocation of callback
. Elements that are appended to the typed array after the call to findIndex
begins will not be visited by callback
. If an existing, unvisited element of the typed array is changed by callback
, its value passed to the visiting callback
will be the value at the time that findIndex
visits that element's index; elements that are deleted are not visited.
Examples
Find the index of a prime number in a typed array
The following example finds the index of an element in the typed array that is a prime number (or returns -1 if there is no prime number).
function isPrime(element, index, array) { var start = 2; while (start <= Math.sqrt(element)) { if (element % start++ < 1) { return false; } } return element > 1; } var uint8 = new Uint8Array([4, 6, 8, 12]); var uint16 = new Uint16Array([4, 6, 7, 12]); console.log(uint8.findIndex(isPrime)); // -1, not found console.log(uint16.findIndex(isPrime)); // 2
Polyfill
TypedArray.prototype.findIndex = Array.prototype.findIndex = Array.prototype.findIndex || function(evaluator, thisArg) { 'use strict'; if (!this) { throw new TypeError('Array.prototype.some called on null or undefined'); } if (typeof(evaluator) !== 'function') { if (typeof(evaluator) === 'string') { // Attempt to convert it to a function if ( ! (evaluator = eval(evaluator)) ){ throw new TypeError(); } } else { throw new TypeError(); } } var i; if (thisArg === undefined) { // Optimize for thisArg for (i in this) { if (evaluator(this[i], i, this)) { return i; } } return -1; } for (i in this) { if (evaluator.call(thisArg, this[i], i, this)) { return i; } } return -1; };
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of '%TypedArray%.prototype.findIndex' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of '%TypedArray%.prototype.findIndex' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | No support | 37.0 (37.0) | 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 | 37.0 (37.0) | No support | No support | No support |