docs: function mergeSort(array, comparefn) {
          var length = array.length,
              middle,
              front,
              back,
              val;
  
          if (length < 2) {
              val = $slice(array);
          } else {
              middle = ceil(length / 2);
              front = $slice(array, 0, middle);
              back = $slice(array, middle);
              val = merge(mergeSort(front, comparefn), mergeSort(back, comparefn), comparefn);
          }
  
          return val;
      }