SOURCE

function quickSort(arr){
  if(arr.length<=1){return arr};
  var mid = Math.floor((arr.length-1)/2);
  var q = arr.splice(mid,1)[0];
  var left = [];
  var right = [];
  for(var i = 0;i<arr.length;i++){
    if(arr[i]<q){
      left.push(arr[i]);
    }
    else if(arr[i]>=q){
      right.push(arr[i]);
    }
  };
  return quickSort(left).concat([q],quickSort(right));
}
console.log(quickSort([2,5,3,2,1,6,3,9,11,33,4]))