递归版快速排序-JS代码

     "use strict"
     var arr1=[11,21,3,4,0];
     function qSort(arr){
         var mid,left,right,len,i,j,emptyArr,emptyArr2;
         len = arr.length;
         left = [];
         right = [];
         emptyArr=[];
         emptyArr2=[];
         j = 0;
         if (len < 2){
             return arr
         }else{
             mid = arr[0];
             for (i=1; i<len; i++){
                 if (arr[i] < mid){
                     left[j] = arr[i]
                     j++
                 }
             }
             j = 0;
             for (i=1; i<len; i++){
                 if (arr[i] >= mid){
                     right[j] = arr[i]
                     j++
                 }
             }
             emptyArr2[0] = mid;
             return emptyArr.concat(qSort(left), emptyArr2, qSort(right))
         }
     }

     console.log(qSort(arr1))