Generating Calendars Programmatically: Harder Than You Think

Every developer thinks building a calendar is a weekend project. You render a 7-column grid, fill in the days, done. Then you discover that February sometimes has 29 days, that months start on different weekdays, that some locales start the week on Monday, that timezone offsets can make the same instant fall on two different dates, and that the JavaScript Date object will silently accept February 30th and return March 2nd instead of throwing an error. I've built more calendar components than I'd like to admit, and every one of them taught me something I didn't expect about date handling. The basic algorithm The core problem is: given a month and year, generate a grid showing which day of the week each date falls on. Here's the logic: Find the first day of the month (what weekday it starts on). Find the total number of days in the month. Fill a 6x7 grid (6 weeks, 7 days) with the appropriate numbers, including trailing days from the previous month and leading days of the next month. fun