code: function makeAs(input, model) {
          var res, diff;
          if (model._isUTC) {
              res = model.clone();
              diff = (moment.isMoment(input) || isDate(input) ?
                      +input : +moment(input)) - (+res);
              // Use low-level api, because this fn is low-level api.
              res._d.setTime(+res._d + diff);
              moment.updateOffset(res, false);
              return res;
          } else {
              return moment(input).local();
          }
      }
docs: Return a moment from input, that is local/utc/utcOffset equivalent to model.