quickSort.js

'use strict';

var arr = [6, 5, 3, 1, 8, 7, 2, 4];

function partition(arr, lp, rp) {
  var middle = Math.floor((lp + rp) / 2),
       pivot = arr[middle],
       temp;

  while (lp <= rp) {
    while (arr[lp] < pivot) lp++;
    while (arr[rp] > pivot) rp--;

    if (lp <= rp) {
      temp = arr[lp];
      arr[lp] = arr[rp];
      arr[rp] = temp;

      lp++;
      rp--;
    }
  }
  return lp;
}

function quickSort(arr, lp, rp) {
  var index;

  lp = lp || 0;
  rp = rp || arr.length - 1;

  if (arr.length > 1) {
    index = partition(arr, lp, rp);
    if (lp < index - 1)
      quickSort(arr, lp, index - 1);

    if (index < rp)
      quickSort(arr, index, rp);
  }
  return arr;
}

console.log(quickSort(arr));