The findLastIndex() method of TypedArray instances iterates the typed array in reverse order and returns the index of the first element that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned. This method has the same algorithm as Array.prototype.findLastIndex.
Syntax
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:
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
findLastIndex()was called upon.
- : The typed array
- : 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:
thisArg- : A value to use as
thiswhen executingcallbackFn. See iterative methods.
- : A value to use as
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.
function isPrime(element) {
if (element % 2 === 0 || element < 2) {
return false;
}
for (let factor = 3; factor <= Math.sqrt(element); factor += 2) {
if (element % 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