QuickSort in JS

quickSort.js

function quickSort (arr) {
  if(arr.length <= 1) {
    return arr;
  }

  var pivot = choosePivot(arr);
  var divider = divide(arr, pivot);
  var a1 = quickSort(arr.slice(0, divider));
  var a2 = quickSort(arr.slice(divider + 1, arr.length));
  a1.push(arr[divider]);
  return a1.concat(a2);
}

// choosing middle value between first, second and last elements
function choosePivot (arr) {
  var l = arr.length - 1;

  if(arr.length <= 2) {
    return 0;
  }

  return (arr[0] >= arr[1] && arr[0] <= arr[l]) || (arr[0] <= arr[1] && arr[0] >= arr[l]) ? 0 :
        (arr[1] >= arr[0] && arr[1] <= arr[l]) || (arr[1] <= arr[0] && arr[1] >= arr[l]) ? 1 : l;
}

function divide (arr, pivot) {
  // swap pivot to the beginning
  tmp = arr[0];
  arr[0] = arr[pivot];
  arr[pivot] = tmp;

  var p1 = 1,
      p2 = arr.length - 1,
      pivotVal = arr[0],
      tmp = null;

  while (p1 < p2) {
    if(arr[p1] > pivotVal) {
      if(arr[p2] <= pivotVal) {
        // swap
        tmp = arr[p1];
        arr[p1] = arr[p2];
        arr[p2] = tmp;
      }
      --p2;
    } else {
      ++p1;
    }
  }

  p1 = arr[p1] > pivotVal ? p1 - 1 : p1;

  // swap pivot to proper position
  tmp = arr[p1];
  arr[p1] = arr[0];
  arr[0] = tmp;

  return p1;
}

console.log(quickSort([9,3,1,6,65,32,2,1,1,4,9]));