deepFlatten javascript Code Snippet in 2025
arrayrecursionintermediate
Last Updated: 29 November 2025
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.
const deepFlatten = arr =>
[].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));deepFlatten([1, [2], [[3], 4], 5]); // [1, 2, 3, 4, 5]
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