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.`.
17 lines
416 B
Markdown
17 lines
416 B
Markdown
### indexOfAll
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Returns all indices of `val` in an array.
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If `val` never occurs, returns `[]`.
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Use `Array.prototype.reduce()` to loop over elements and store indices for matching elements.
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Return the array of indices.
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```js
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const indexOfAll = (arr, val) => arr.reduce((acc, el, i) => (el === val ? [...acc, i] : acc), []);
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```
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```js
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indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
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indexOfAll([1, 2, 3], 4); // []
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```
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