Use stack to store, just change it

function qsort_with_loop(arr) {
  let stack = [];

  stack.push([0, arr.length - 1]);

  while (stack.length) {
    let _ = stack.pop();
    let i = l = _[0];
    let j = r = _[1];
    let mid = arr[(i + j) >> 1];

    do {
      while (arr[i] < mid) ++i;
      while (arr[j] > mid) --j;
      if (i <= j) {
        let t = arr[i];
        arr[i] = arr[j];
        arr[j] = t;
        ++i;
        --j;
      }
    } while (i <= j);

    if (i < r) stack.push([i, r]);
    if (l < j) stack.push([l, j]);
  }
}

Written two versions, please compare: https://jsfiddle.net/hsfzxjy/ob8x16uz/4/

You can use the stack to store state, which is the essence of recursion in high-level languages

import java.util.Stack;
//快速排序的非递归实现，利用系统的栈stack
public class QuickSortNonRecursion {
     public static void main(String[] args) {
         QuickSortNonRecursion qsnr = new QuickSortNonRecursion();
         int[] array = {0, 2, 11, 121, 18, 99, 3, 5, 101, 22, 9, 100};
         qsnr.quicksort(array);
          for (int i : array) {
                System.out.print(i + "  ");
          }
        }
                 
        public void quicksort(int[] array) {
            if (array == null || array.length == 1) return;
            //存放开始与结束索引
            Stack<Integer> s = new Stack<Integer>(); 
            //压栈       
            s.push(0); 
            s.push(array.length - 1); 
            //利用循环里实现
            while (!s.empty()) { 
                int right = s.pop(); 
                int left = s.pop(); 
                //如果最大索引小于等于左边索引，说明结束了
                if (right <= left) continue; 
                         
                int i = partition(array, left, right); 
                if (left < i - 1) {
                    s.push(left);
                    s.push(i - 1);
                } 
                if (i + 1 < right) {
                    s.push(i+1);
                    s.push(right);
                }
            } 
        }
        //找到轴心，进行交换
        public int partition (int[] data, int first, int end)
        {
            int temp;
            int i=first,j=end;
            if(first<end)
            {
                temp=data[i];
                //当i=j的时候，则说明扫描完成了
                while(i<j)
                {
                    //从右边向左边扫描找到一个小于temp的元素
                    while(j>i&&data[j]>temp)j--;
                    if(i<j)
                    {
                        //将该元素赋值给temp
                        data[i]=data[j];
                        //赋值后就应该将i+1指向下一个序号
                        i++;
                    }
                           
                    //然后从左边向右边开始扫描，找到一个大于temp的元素
                    while(i<j&&temp>data[i])i++;
                    if(i<j)
                    {
                        //将该元素赋值给temp
                        data[j]=data[i];
                        //赋值后就应该将j-1指向前一个序号
                        j--;
                    }
                }
                //将轴数据放在i位置中
                data[i]=temp;
            }
            return i;
        }
    }