QuickSort implementation in JavaScript

quicksort.js

var quickSort = function(array, left, right){

  var leftIndex = partition(array, left, right);

  if (left < leftIndex - 1){
    quickSort(array, left, leftIndex-1);
  }
  
  if (right > leftIndex){
    quickSort(array, leftIndex, right);
  }
   
  return array;
}

var swap = function(array, left, right){
  var temp;
  temp = array[leftIndex];
  array[leftIndex] = array[rightIndex];
  array[rightIndex] = temp;    
}

var partition = function(array, left, right){
  var pivotIndex = Math.floor( (left + right) / 2);
  var pivot = array[pivotIndex];

  leftIndex = left;
  rightIndex = right;
  
  while (leftIndex <= rightIndex){
    while(array[leftIndex] < pivot){
      leftIndex++;
    }
    
    while(array[rightIndex] > pivot){
      rightIndex--;
    }
    
    if (leftIndex <= rightIndex){
      swap(array, left, right);
      leftIndex++;
      rightIndex--;
    }
  }
  return leftIndex;
}