function quickSort(arr){  if(arr.length <= 1) return arr;//判断是否有效数组  var cut = Math.floor(arr.length/2);//取中间下标  var left = [],right = [];  var num = arr.splice(cut,1)[0];//取基准值  for(var i = 0;i < arr.length;i ++){    if(arr[i] < num){      left.push(arr[i]);//小的放左边    }else {      right.push(arr[i]);//大的放右边    }  }  return quickSort(left).concat(num,quickSort(right));//递归}