TypedArray.prototype.findLastIndex() - JavaScript | MDN
Try it
function isNegative(element /*, index, array */) {
return element < 0;
}
const int8 = new Int8Array([10, -20, 30, -40, 50]);
console.log(int8.findLastIndex(isNegative));
// Expected output: 3
Syntax
js
findLastIndex(callbackFn)
findLastIndex(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 last (highest-index) element in the typed array that passes the test.
Otherwise -1 if no matching element is found.
Description
See Array.prototype.findLastIndex() for more details. This method is not generic and can only be called on typed array instances.
Examples
Find the index of the last prime number in a typed array
The following example returns the index of the last 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;
}
let uint8 = new Uint8Array([4, 6, 8, 12]);
console.log(uint8.findLastIndex(isPrime));
// -1 (no primes in array)
uint8 = new Uint8Array([4, 5, 7, 8, 9, 11, 12]);
console.log(uint8.findLastIndex(isPrime));
// 5
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.findlastindex |