TypedArray.prototype.findIndex()

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.

Try it

Syntax

findIndex(callbackFn)
findIndex(callbackFn, thisArg)

Parameters

callbackFn

A function to execute for each element in the typed array. It should return a truthy value to indicate a matching element has been found, and a falsy value otherwise. The function is called with the following 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

A value to use as this when executing callbackFn. See iterative methods.

Return value

An index in the array if an element passes the test; otherwise, -1.

Description

The findIndex() method executes the callbackFn function once for each element present in the typed array until it finds one where callbackFn returns a true value. If such an element is found, findIndex() immediately returns the index of that element. Otherwise, findIndex() returns -1. callbackFn 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.

callbackFn 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 callbackFn. Elements that are appended to the typed array after the call to findIndex() begins will not be visited by callbackFn. If an existing, unvisited element of the typed array is changed by callbackFn, its value passed to the visiting callbackFn 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) {
  let start = 2;
  while (start <= Math.sqrt(element)) {
    if (element % start++ < 1) {
      return false;
    }
  }
  return element > 1;
}

const uint8 = new Uint8Array([4, 6, 8, 12]);
const uint16 = new Uint16Array([4, 6, 7, 12]);

console.log(uint8.findIndex(isPrime)); // -1, not found
console.log(uint16.findIndex(isPrime)); // 2

Specifications

Specification
ECMAScript Language Specification
# sec-%typedarray%.prototype.findindex

Browser compatibility

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See also