11 lines
346 B
Markdown
11 lines
346 B
Markdown
### Deep flatten array
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Use recursion.
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Use `Array.concat()` with an empty array (`[]`) and the spread operator (`...`) to flatten an array.
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Rrecursively flatten each element that is an array.
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```js
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const deepFlatten = arr => [].concat(...arr.map(v => Array.isArray(v) ? deepFlatten(v) : v));
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// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
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```
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