Quick sort.

quickSort

function quickSort(array, start, end){

   var leftIndex = partition(array, start, end);
   
   if (start < leftIndex-1){
       quickSort(array, start, leftIndex-1);
   }
   
   if (start > leftIndex){
       quickSort(array, leftIndex, end);
   }
    
   return array;
}

function partition(array, start, end){
    var mid = Math.floor( (start + end) / 2 );
    var pivot = array[mid];
    var left = start;
    var right = end;
    
    while (left <= right){
        while(array[left] < pivot){
            left++;
        }
        
        while(array[right] > pivot){
            right--;
        }
        
        if (left <= right){
            swap(array, left, right);
            left++;
            right--;
        }
    }
    
    return left;
}

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

console.log(quickSort([5, 3, 4, 1, 2, 6], 0, 4));