function quickSort(arr){
  var pivot = arr[Math.floor(Math.random() * arr.length)];
  console.log("piv: ", pivot);
  if (arr.length < 2){
    return arr;
  }
  var smaller = [];
  var bigger = [];
  var pivots = [];
  arr.forEach(function(i){
    if (i < pivot) {
      smaller.push(i)
    } else if (i > pivot) {
      bigger.push(i)
    } else {
      pivots.push(i)
    }
  })
  return [
    ...quickSort(smaller),
    ...pivots,
    ...quickSort(bigger)
  ];
}

console.log(quickSort([1,5,3,7,8,2,9,3,5]));