function quickSort(arr) {
  if (arr.length == 0) return [];
  let a = [],
    b = [],
    p = arr[0];

  for (let i = 1; i < arr.length; i++) {
    if (arr[i] < p) a.push(arr[i]);
    else b.push(arr[i]);
  }
  return quickSort(a).concat(p, quickSort(b));
}
quickSort(arr);