TypedArray.prototype.findIndex() - JavaScript | MDN
Try it
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
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:
thisArgOptional-
A value to use as
thiswhen executingcallbackFn. See iterative methods.
Return value
The index of the first element in the typed array that passes the test. Otherwise, -1.
Description
See 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.
js
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
| Specification |
|---|
| ECMAScript® 2027 Language Specification # sec-%typedarray%.prototype.findindex |