eachNthDayOfMonth.js

const getSpecifiedDay = {
  oncePerMonth: (fromDate, dayOfWeek, numberOfTimes, startHours, endHours) => {

    // Get first day of the month by given fromDate
    const currentMonth = moment(fromDate).startOf('month');

    // Get desired dayOfWeek of currentMonth's first week
    const firstDayInMonth = currentMonth.clone().weekday(dayOfWeek);

    // Check if firstDayInMonth is in the given month
    if (firstDayInMonth.month() !== currentMonth.month()) {
      numberOfTimes++;
    }

    return firstDayInMonth.add(--numberOfTimes, 'weeks');
  },
  oncePerWeek: (fromDate, dayOfWeek, startHours, endHours) => {
  
  }
}