JavaScript age calculators crash on Feb 29 birthdays: because nothing says 'ship it' like making leap year kids eternally 28

A recent article highlights the common errors in calculating age in JavaScript, particularly when dealing with leap years, February 29 birthdays, and the January 31 trap. To accurately calculate age, it is essential to normalize dates to midnight local time and define a policy for handling February 29 birthdays in non-leap years. A simple and dependable algorithm can be used to compute years, months, and days between two calendar dates. The algorithm involves calculating tentative years, setting an anchor date for the last birthday, and walking forward month-by-month to determine the remaining days. The implementation in TypeScript includes functions to normalize dates and calculate age, with tests to ensure correctness for various scenarios, including edge cases like January 31 and February 29 birthdays. By following this approach, developers can create accurate age calculators without relying on external libraries, which is significant in the software development industry where date and time calculations are crucial.