TypedArray.prototype.findLast()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since August 2022.
The findLast()
method of TypedArray
instances iterates the typed array in reverse order and returns the value of the first element that satisfies the provided testing function. If no elements satisfy the testing function, undefined
is returned. This method has the same algorithm as Array.prototype.findLast()
.
Try it
function isNegative(element /*, index, array */) {
return element < 0;
}
const int8 = new Int8Array([10, 0, -10, 20, -30, 40, 50]);
console.log(int8.find(isNegative));
// Expected output: -30
Syntax
findLast(callbackFn)
findLast(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:
thisArg
Optional-
A value to use as
this
when executingcallbackFn
. See iterative methods.
Return value
The last (highest-index) element in the typed array that satisfies the provided testing function; undefined
if no matching element is found.
Description
See Array.prototype.findLast()
for more details. This method is not generic and can only be called on typed array instances.
Examples
Find the last prime number in a typed array
The following example returns the last element in the typed array that is a prime number, or undefined
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.findLast(isPrime)); // undefined (no primes in array)
uint8 = new Uint8Array([4, 5, 7, 8, 9, 11, 12]);
console.log(uint8.findLast(isPrime)); // 11
All elements are visited and may be modified by the callback
The following examples show that all elements are visited, and that the value passed to the callback is their value when visited:
// Declare array with no elements at indexes 2, 3, and 4
// The missing elements will be initialized to zero.
const uint8 = new Uint8Array([0, 1, , , , 5, 6]);
// Iterate through the elements in reverse order.
// Note that all elements are visited.
uint8.findLast((value, index) => {
console.log(`Visited index ${index} with value ${value}`);
});
// Shows all indexes, including deleted
uint8.findLast((value, index) => {
// Modify element 3 on first iteration
if (index === 6) {
console.log("Set uint8[3] to 44");
uint8[3] = 44;
}
// Element 3 is still visited but will have a new value.
console.log(`Visited index ${index} with value ${value}`);
});
// Visited index 6 with value 6
// Visited index 5 with value 5
// Visited index 4 with value 0
// Visited index 3 with value 0
// Visited index 2 with value 0
// Visited index 1 with value 1
// Visited index 0 with value 0
// Set uint8[3] to 44
// Visited index 6 with value 6
// Visited index 5 with value 5
// Visited index 4 with value 0
// Visited index 3 with value 44
// Visited index 2 with value 0
// Visited index 1 with value 1
// Visited index 0 with value 0
Specifications
Specification |
---|
ECMAScript® 2025 Language Specification # sec-%typedarray%.prototype.findlast |
Browser compatibility
Report problems with this compatibility data on GitHubdesktop | mobile | server | ||||||||||||
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findLast |
Legend
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- Full support
- Full support
- No support
- No support
See also
- Polyfill of
TypedArray.prototype.findLast
incore-js
- JavaScript typed arrays guide
TypedArray
TypedArray.prototype.find()
TypedArray.prototype.findIndex()
TypedArray.prototype.findLastIndex()
TypedArray.prototype.includes()
TypedArray.prototype.filter()
TypedArray.prototype.every()
TypedArray.prototype.some()
Array.prototype.findLast()