Flatten an array of arbitrarily nested arrays of integers into a flat array of integers.

Flatten an array

function isArray(arr) {
  return Object.prototype.toString.call(arr) === '[object Array]';
}

function arrToFlat(arr, arrToReturn) {
  if (!isArray(arr)) {
    return false;
  }
  if (!arrToReturn) {
    arrToReturn = [];
  }
  var i = 0, max = arr.length;
  for (; i < max; i++) {
    if (isArray(arr[i])) {
      arrToFlat(arr[i], arrToReturn);
    } else {
      arrToReturn.push(arr[i]);
    }
  }
  return arrToReturn;
}


console.log(arrToFlat([[1, 2, [3]], 4, [5, 6, 7, [8]]])); // output [1, 2, 3, 4, 5, 6, 7, 8]
console.log(arrToFlat([1, 2, 3, [4]])); // output [1, 2, 3, 4]