Flatten n-depth array es6

flat.js

// Checks the equality of arrays based on value
const assertEqual = (arr1, arr2) => {
  if (arr1.length !== arr2.length)
    return false;
  for (var i = arr1.length; i--;) {
    if (arr1[i] !== arr2[i])
      return false;
  }

  return true;
}

// Recursive algorithm to flatten n nested arrays
const flat = list => list.reduce(
  (a, b) => a.concat(Array.isArray(b) ? flat(b) : b), []
);

// Tests
console.log(assertEqual(flat([1, 2, [23, 5, 2], [[6], [2, 3, 6]]]), [1, 2, 23, 5, 2, 6, 2, 3, 6]))
console.log(assertEqual(flat([[[[[1, 3, 4, [334, 5, 77, 91]]]]], 234]), [1, 3, 4, 334, 5, 77, 91, 234]))