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30-seconds-of-code/snippets/indexOfAll.md
Robert Mennell 272b6588b3 indexOfAll.md returns a functions with shadow vars
It returned a function that accepted the same arguments again that when run again with the same inputs would eventually result
2018-08-02 12:57:02 -07:00

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