code: function(year, monthIndex, day) {
              var date = this._validate(year, month, day, $.calendars.local.invalidDate);
              year = this._validateYear(date.year());
              monthIndex = date.month();
              day = date.day();
  
              var isIntercalary = this.isIntercalaryMonth(year, monthIndex);
              var month = this.toChineseMonth(year, monthIndex);
  
              var solar = toSolar(year, month, day, isIntercalary);
  
              return gregorianCalendar.toJD(solar.year, solar.month, solar.day);
          }
docs: Retrieve the Julian date equivalent for this date,
  i.e. days since January 1, 4713 BCE Greenwich noon.
  @memberof ChineseCalendar
  @param year {CDate|number} The date to convert or the year to convert.
  @param [monthIndex] {number} The month index to convert.
  @param [day] {number} The day to convert.
  @return {number} The equivalent Julian date.
  @throws Error if an invalid date or a different calendar used.