30-seconds-of-code/snippets/flatten-array.md

Flatten array

Use recursion. Use reduce() to get all elements that are not arrays, flatten each element that is an array.

const flatten = arr =>
  arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
// flatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]