TypedArray.prototype.findIndex()

The findIndex() method of {{jsxref("TypedArray")}} instances returns the index of the first element in a typed array that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned. This method has the same algorithm as {{jsxref("Array.prototype.findIndex()")}}.

{{InteractiveExample("JavaScript Demo: TypedArray.prototype.findIndex()")}}

```js interactive-example function isNegative(element, index, array) { return element < 0; }

const int8 = new Int8Array([10, -20, 30, -40, 50]);

console.log(int8.findIndex(isNegative)); // Expected output: 1

## Syntax

```js-nolint
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_inline}}
• : A value to use as this when executing callbackFn. See iterative methods.

Return value#

The index of the first element in the typed array that passes the test. Otherwise, -1.

Description#

See {{jsxref("Array.prototype.findIndex()")}} for more details. This method is not generic and can only be called on typed array instances.

Examples#

Find the index of the first prime number in a typed array#

The following example returns the index of the first element in the typed array that is a prime number, or -1 if there is no prime number.

function isPrime(n) {
  if (n < 2) {
    return false;
  }
  if (n % 2 === 0) {
    return n === 2;
  }
  for (let factor = 3; factor * factor <= n; factor += 2) {
    if (n % factor === 0) {
      return false;
    }
  }
  return true;
}

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

[!NOTE] The isPrime() implementation is for demonstration only. For a real-world application, you would want to use a heavily memoized algorithm such as the Sieve of Eratosthenes to avoid repeated calculations.

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• Polyfill of TypedArray.prototype.findIndex in core-js
• JavaScript typed arrays guide
• {{jsxref("TypedArray")}}
• {{jsxref("TypedArray.prototype.find()")}}
• {{jsxref("TypedArray.prototype.findLast()")}}
• {{jsxref("TypedArray.prototype.findLastIndex()")}}
• {{jsxref("TypedArray.prototype.indexOf()")}}
• {{jsxref("TypedArray.prototype.lastIndexOf()")}}
• {{jsxref("Array.prototype.findIndex()")}}