function QuickSort(list) {
  if (list.length < 2) {
    return list;
  } 
  
  let leftList = [];
  let rightList = [];
  const pivotList = [];
  const pivot = list[0];

  for (let x = 0; x < list.length; x++) {
    if(list[x] < pivot) {
      leftList.push(list[x]);
    } else if (list[x] === pivot) {
      pivotList.push(list[x]);
    } else {
      rightList.push(list[x]);
    }
  }

  leftList = QuickSort(leftList);
  rightList = QuickSort(rightList);

  return leftList.concat(pivotList, rightList);
}

let sortedList = QuickSort([5,4,1,5,7,5,9,4]);
console.log(sortedList.toString());