_.flattenDeep

Recursively flattens array.

// Underscore/Lodash
_.flattenDeep([1, [2, [3, [4]], 5]]);
// => [1, 2, 3, 4, 5]
 
// Native
const flattenDeep = (arr) => Array.isArray(arr)
  ? arr.reduce( (a, b) => a.concat(flattenDeep(b)) , [])
  : [arr]
 
flattenDeep([1, [[2], [3, [4]], 5]])
// => [1, 2, 3, 4, 5]
 
// Native(ES2019)
[1, [2, [3, [4]], 5]].flat(Infinity)
// => [1, 2, 3, 4, 5]

Browser Support

46.0 ✔	✔	16.0 ✔	✖	37.0 ✔	7.1 ✔

Browser Support for Array.prototype.flat()

69 ✔	✖	62 ✔	✖	56 ✔	12 ✔