How to handle daylight saving time (DST) transitions in JavaScript?

1. Determine if DST is currently in effect:

   • JavaScript provides the getTimezoneOffset() method which returns the time zone offset in minutes for the current locale.
   • By comparing the current offset with the offset of a known non-DST time (e.g. January 1st), you can determine if DST is in effect.

2. Convert dates and times to UTC:

   • Use the Date.UTC() method to convert all dates and times to UTC. This ensures that DST transitions do not affect the calculations.

3. Use a library:

   • JavaScript libraries like Moment.js or Luxon provide built-in features to handle DST transitions. They offer methods to manipulate and format dates while automatically handling time zone and DST conversions.

4. Adjust date and time calculations manually:

   • When working with specific date and time values, you may need to manually adjust for DST transitions. For example, if a DST transition occurs at 2am on a specific date, any time between 2am and 3am will be an "ambiguous" period. You may need to add or subtract an hour to handle this correctly.

5. Consider using external APIs or services:

   • If precise time keeping is crucial, consider using external APIs or services that provide accurate time zone and DST information, such as the Time Zone database or services like Google Time Zone API.

6. Test and handle edge cases:

   • DST transitions can be complex, and it is important to thoroughly test your code for various scenarios. Consider testing cases like crossing time zone boundaries or handling exceptions like invalid input.

By following these guidelines, you can handle DST transitions in JavaScript and ensure your code works correctly under different time zone and DST configurations.