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javascript/snippets/deep-flatten.md

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+---
+title: Deep flatten array
+type: snippet
+tags: [array,recursion]
+cover: digital-nomad-4
+dateModified: 2020-10-22T20:23:47+03:00
+---
+
+Deep flattens an array.
+
+- Use recursion.
+- Use `Array.prototype.concat()` with an empty array (`[]`) and the spread operator (`...`) to flatten an array.
+- Recursively flatten each element that is an array.
+
+```js
+const deepFlatten = arr =>
+  [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
+```
+
+```js
+deepFlatten([1, [2], [[3], 4], 5]); // [1, 2, 3, 4, 5]
+```