Array.prototype.findLast()
==========================

 The **`findLast()`** method of `Array` instances iterates the 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.

If you need to find:

* the *first* element that matches, use `find()`.
* the *index* of the last matching element in the array, use `findLastIndex()`.
* the *index of a value*, use `indexOf()`.
 (It's similar to `findIndex()`, but checks each element for equality with the value instead of using a testing function.)
* whether a value *exists* in an array, use `includes()`.
 Again, it checks each element for equality with the value instead of using a testing function.
* if any element satisfies the provided testing function, use `some()`.
Try it
------

Syntax
------


```js
findLast(callbackFn)
findLast(callbackFn, thisArg)
```

### Parameters

`callbackFn`

A function to execute for each element in the 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 array.

`index`

The index of the current element being processed in the array.

`array`

The array `findLast()` was called upon.


`thisArg` Optional

A value to use as `this` when executing `callbackFn`. See iterative methods.

### Return value

The last (highest-index) element in the array that satisfies the provided testing function; `undefined` if no matching element is found.

Description
-----------

The `findLast()` method is an iterative method. It calls a provided `callbackFn` function once for each element in an array in descending-index order, until `callbackFn` returns a truthy value. `findLast()` then returns that element and stops iterating through the array. If `callbackFn` never returns a truthy value, `findLast()` returns `undefined`. Read the iterative methods section for more information about how these methods work in general.

`callbackFn` is invoked for *every* index of the array, not just those with assigned values. Empty slots in sparse arrays behave the same as `undefined`.

The `findLast()` method is generic. It only expects the `this` value to have a `length` property and integer-keyed properties.

Examples
--------

### Find last object in an array matching on element properties

This example shows how you might create a test based on the properties of array elements.


```js
const inventory = [
  { name: "apples", quantity: 2 },
  { name: "bananas", quantity: 0 },
  { name: "fish", quantity: 1 },
  { name: "cherries", quantity: 5 },
];

// return true inventory stock is low
function isNotEnough(item) {
  return item.quantity < 2;
}

console.log(inventory.findLast(isNotEnough));
// { name: "fish", quantity: 1 }
```


#### Using arrow function and destructuring

The previous example might be written using an arrow function and object destructuring:


```js
const inventory = [
  { name: "apples", quantity: 2 },
  { name: "bananas", quantity: 0 },
  { name: "fish", quantity: 1 },
  { name: "cherries", quantity: 5 },
];

const result = inventory.findLast(({ quantity }) => quantity < 2);

console.log(result);
// { name: "fish", quantity: 1 }
```

### Find the last prime number in an array

The following example returns the last element in the array that is a prime number, or `undefined` if there is no prime number.


```js
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;
}

console.log([4, 6, 8, 12].findLast(isPrime)); // undefined, not found
console.log([4, 5, 7, 8, 9, 11, 12].findLast(isPrime)); // 11
```

### Using the third argument of callbackFn

The `array` argument is useful if you want to access another element in the array, especially when you don't have an existing variable that refers to the array. The following example first uses `filter()` to extract the positive values and then uses `findLast()` to find the last element that is less than its neighbors.


```js
const numbers = [3, -1, 1, 4, 1, 5, 9, 2, 6];
const lastTrough = numbers
  .filter((num) => num > 0)
  .findLast((num, idx, arr) => {
    // Without the arr argument, there's no way to easily access the
    // intermediate array without saving it to a variable.
    if (idx > 0 && num >= arr[idx - 1]) return false;
    if (idx < arr.length - 1 && num >= arr[idx + 1]) return false;
    return true;
  });
console.log(lastTrough); // 2
```

### Using findLast() on sparse arrays

Empty slots in sparse arrays *are* visited, and are treated the same as `undefined`.


```js
// Declare array with no elements at indexes 2, 3, and 4
const array = [0, 1, , , , 5, 6];

// Shows all indexes, not just those with assigned values
array.findLast((value, index) => {
  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 undefined
// Visited index 3 with value undefined
// Visited index 2 with value undefined
// Visited index 1 with value 1
// Visited index 0 with value 0

// Shows all indexes, including deleted
array.findLast((value, index) => {
  // Delete element 5 on first iteration
  if (index === 6) {
    console.log(`Deleting array[5] with value ${array[5]}`);
    delete array[5];
  }
  // Element 5 is still visited even though deleted
  console.log(`Visited index ${index} with value ${value}`);
});
// Deleting array[5] with value 5
// Visited index 6 with value 6
// Visited index 5 with value undefined
// Visited index 4 with value undefined
// Visited index 3 with value undefined
// Visited index 2 with value undefined
// Visited index 1 with value 1
// Visited index 0 with value 0
```

### Calling findLast() on non-array objects

The `findLast()` method reads the `length` property of `this` and then accesses each property whose key is a nonnegative integer less than `length`.


```js
const arrayLike = {
  length: 3,
  0: 2,
  1: 7.3,
  2: 4,
  3: 3, // ignored by findLast() since length is 3
};
console.log(
  Array.prototype.findLast.call(arrayLike, (x) => Number.isInteger(x)),
); // 4
```

Specifications
--------------

| Specification |
| --- |
| ECMAScript Language Specification # sec-array.prototype.findlast |

Browser compatibility
---------------------

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See also
--------

* Polyfill of `Array.prototype.findLast` in `core-js`
* Indexed collections guide
* `Array`
* `Array.prototype.find()`
* `Array.prototype.findIndex()`
* `Array.prototype.findLastIndex()`
* `Array.prototype.includes()`
* `Array.prototype.filter()`
* `Array.prototype.every()`
* `Array.prototype.some()`
* `TypedArray.prototype.findLast()`