Generate a simple calendar which is an array of arrays

simple-calendar.ts

/**
 * Generates a simple Calendar formatted as an array of arrays
 * @param year Year for which calendar month is generated
 * @param month Calendar month to be generated
 * @param startWeekMonday Optional offset -- defaults to false (week starts on Sunday)
 * @returns Main array (month) of arrays (weeks) of days
 * @see Based on algorithm by github:lukeed/calendarize
 */
private generateMonthCalendar(year: number, month: number, startWeekMonday = false) {
  const res: number[][] = [];

  const weekOffset = startWeekMonday ? 1 : 0;
  let dayOfWeek = new Date(year, month, 1 - weekOffset).getDay();
  const daysInMonth = new Date(year, month + 1, 0).getDate();

  let day = 0;
  while (day < daysInMonth) {
    const week = Array(7);
    for (let weekdayIterator = 0; weekdayIterator < 7;) {
      while (weekdayIterator < dayOfWeek) {
        week[weekdayIterator++] = 0;
      }
      week[weekdayIterator++] = ++day > daysInMonth ? 0 : day;
      dayOfWeek = 0;
    }
    res.push(week);
  }

  return res;
}