code: function monthrange(year, month) {
        if(month < 1 || month > 12) {
          throw new IllegalMonthError();
        }
  
        var day1 = weekday(year, month, 1);
        var ndays = _DAYS_IN_MONTH[month] + (month === 2 && isleap(year));
  
        return [day1, ndays];
      }
docs: Return starting weekday (0-6 ~ Mon-Sun) and number of days (28-31) for
  year, month.
  
  @param {Number} year
  @param {Number} month
  @throws {IllegalMonthError} If the provided month is invalid.
  @api public