8ee50178f3
Correct: `Array.from()` (it’s a static method) Incorrect: `Array.join()` (doesn’t exist; it’s a prototype method) This patch uses the common `#` syntax to denote `.prototype.`.
19 lines
560 B
Markdown
19 lines
560 B
Markdown
### findLastIndex
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Returns the index of the last element for which the provided function returns a truthy value.
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Use `Array.prototype.map()` to map each element to an array with its index and value.
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Use `Array.prototype.filter()` to remove elements for which `fn` returns falsey values, `Array.prototype.pop()` to get the last one.
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```js
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const findLastIndex = (arr, fn) =>
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arr
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.map((val, i) => [i, val])
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.filter(([i, val]) => fn(val, i, arr))
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.pop()[0];
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```
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```js
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findLastIndex([1, 2, 3, 4], n => n % 2 === 1); // 2 (index of the value 3)
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```
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