code: function (items) {
      if (items.length < 2) {
          return items;
      }
  
      var middle = Math.floor(items.length / 2);
  
      return merge(
          mergeSort(items.slice(0, middle)),
          mergeSort(items.slice(middle))
      );
  }
docs: Take an array and slice it in halves, sorting each half along the way.
  
  @param  {array} items
  @return {array} the sorted array