code: function startDoyWeek(aFirstDayOfWeek) {
        var firstDow = aFirstDayOfWeek || ICAL.Time.SUNDAY;
        var delta = this.dayOfWeek() - firstDow;
        if (delta < 0) delta += 7;
        return this.dayOfYear() - delta;
      }
docs: First calculates the start of the week, then returns the day of year for
  this date. If the day falls into the previous year, the day is zero or negative.
  
  @param {ICAL.Time.weekDay=} aFirstDayOfWeek
  The week start weekday, defaults to SUNDAY
  @return {Number}     The calculated day of year