如何使用 JavaScript 实现快速排序？

/* 如何使用 JavaScript 实现快速排序？ */
function quickSort(arr, left, right) {
  var len = arr.length,
    partitionIndex,
    left = typeof left != 'number' ? 0 : left,
    right = typeof right != 'number' ? len - 1 : right;
  if (left < right) {
    partitionIndex = partition(arr, left, right);
    quickSort(arr, left, partitionIndex - 1);
    quickSort(arr, partitionIndex + 1, right);
  }
  return arr;
}
function partition(arr, left, right) {
  var pivot = left,
    index = pivot + 1;
  for (var i = index; i <= right; i++) {
    if (arr[i] < arr[pivot]) {
      swap(arr, i, index);
      index++;
    }
  }
  swap(arr, pivot, index - 1);
  return index - 1;
}
function swap(arr, i, j) {
  var temp = arr[i];
  arr[i] = arr[j];
  arr[j] = temp;
}