19 lines
559 B
Markdown
19 lines
559 B
Markdown
### findLastIndex
|
|
|
|
Returns the index of the last element for which the provided function returns a truthy value.
|
|
|
|
Use `Array.prototype.map()` to map each element to an array with its index and value.
|
|
Use `Array.prototype.filter()` to remove elements for which `fn` returns falsy values, `Array.prototype.pop()` to get the last one.
|
|
|
|
```js
|
|
const findLastIndex = (arr, fn) =>
|
|
arr
|
|
.map((val, i) => [i, val])
|
|
.filter(([i, val]) => fn(val, i, arr))
|
|
.pop()[0];
|
|
```
|
|
|
|
```js
|
|
findLastIndex([1, 2, 3, 4], n => n % 2 === 1); // 2 (index of the value 3)
|
|
```
|