dayOptions.js

  dayOptions() {
    const { date } = this.props;
    const month = date.getMonth();
    const year = date.getFullYear();
    const possibleDays = makeRange(1, 31);
    const actualDays = possibleDays.filter(day => {
      // We take an advantage of the fact that if you
      // specify the 'invalid' date like 31st of February       
      // it'll automatically switch to the next month.
      // So new Date(2016, 1, 90) === Apr 30th 2016

      const possibleDate = new Date(year, month, day);
      return possibleDate.getMonth() === month;
    });

    const actualDayOfWeeks = actualDays.map(day => {
      const date = new Date(year, month, day);
      return date.getDay();
    });

    return zip(actualDays, actualDayOfWeeks).map(
       ([day, dayOfWeek]) => (
         <option value={day}>
           {day} - {dayName(dayOfWeek)}
         </option>);
  }