code: function adjustedIndex(slot) {
                      var undefinedIndex;
  
                      if (!slot) {
                          return undefinedIndex;
                      }
  
                      var delta = 0;
                      while (!slot.firstInSequence) {
                          delta++;
                          slot = slot.prev;
                      }
  
                      return (
                          typeof slot.indexNew === "number" ?
                              slot.indexNew + delta :
                          typeof slot.index === "number" ?
                              slot.index + delta :
                              undefinedIndex
                      );
                  }
docs: Deferred Index Updates Returns the index of the slot taking into account any outstanding index updates