code: function (item, comparer, index, count) {
          index = index || 0;
          count = count || this.length;
          comparer = Comparer.from(comparer);
  
          return binarySearch(this, index, count, item, comparer.compare);
      }
docs: Searches a range of elements in the sorted List for an element using the specified comparer and returns the zero-based index of the element.
  @param {Object} item The object to locate.
  @param {Comparer=} comparer The Comparer implementation to use when comparing elements.
  @param {Number=} index The zero-based starting index of the range to search.
  @param {Number=} count The length of the range to search.
  @returns {Number}