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.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
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 |
---|
ECMAScript (ECMA-262) The definition of '%TypedArray%.prototype.findIndex' in that specification. |
Browser compatibility
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