JavaScript快速排序

function quickSort(arr) {
  let length = arr.length;

  if (length <= 1) {
    return arr;
  }
  let leftArr = [], rightArr = [], q = arr[0];
  for (let i = 1; i < length; i++) {
    let item = arr[i];
    item < q ? leftArr.push(item) : rightArr.push(item);
  }
  return [].concat(quickSort(leftArr), [q], quickSort(rightArr));
}