Odd timezone offset when converting

Question

I am trying to use UTC wherever possible. Now I found the following strange behaviour and I really don't understand what ist happening. It would be great, if someone could give advice.

Note: I write my code in the Google Apps Script Editor.

I use the following code to create a date and get the output in my local timezone:

var testDate = Date.UTC(2022,0,1,0,0,0,0);
Logger.log(Utilities.formatDate(new Date(testDate), 'Europe/Berlin', 'dd.MM.yyyy hh:mm'));

The result is 01.01.2022 01:00 , as expected, because 'Europe/Berlin' is 1 hour behind UTC. So if I wanted the output to be 01.01.2022 00:00 I would try the following:

var testDate = Date.UTC(2021,11,31,23,0,0,0);
Logger.log(Utilities.formatDate(new Date(testDate), 'Europe/Berlin', 'dd.MM.yyyy hh:mm'));

But the result I get is: 01.01.2022 12:00 Can anybody hint me to why my expectation is wrong?

(I hope my English is okay.)

Answer 1

If you wanted to do it the way you're doing it, you'd want 23 (11 p.m. ) for the hour value, not 11 (11 a.m. ).

But if you're trying to format in UTC, I wouldn't play offset games to do this, not least because Berlin isn't always one hour offset from UTC, sometimes it's two hours offset (daylight saving time).¹ Instead, I'd have a formatter that uses the UTC accessors on Date ( getUTCHours , getUTCMonth , etc.) to build the string rather than using the local time version. Either some library, or something that uses Intl.DateTimeFormat . For example:

 const testDate = Date.UTC(2022,0,1,0,0,0,0); const dateTimeFormat = new Intl.DateTimeFormat("de", { timeZone: "UTC", dateStyle: "medium", timeStyle: "short", }).format; // Outputs "01.01.2022, 00:00", which is close to but // not quite the same as your desired format console.log(dateTimeFormat(testDate)); // Outputs your desired format, but may not be flexible across locales const dateFormat = new Intl.DateTimeFormat("de", { timeZone: "UTC", dateStyle: "medium", }).format; const timeFormat = new Intl.DateTimeFormat("de", { timeZone: "UTC", timeStyle: "short", }).format; console.log(`${dateFormat(testDate)} ${timeFormat(testDate)}`);

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¹ Remember that UTC is unchanging, it doesn't have daylight saving time.