Guess should ignore Intl detection bad results

[jou]

Sometimes, the Internationalization API doesn't return sensible values. I encountered that in Chrome for Android, where it returns "CET" instead of a timezone ID when the selected system timezone is using Central European Time.

Currently, I'm removing Intl.DateTimeFormat before calling moment.tz.guess(true) again. That's not really a nice solution, so can an option be added to bypass it?

[SuperMario77]

I also vote for such an option. I work on a cordova app on Windows 10 tablet and there the Microsoft Edge Browser Engine will be used. I noticed that the call to "Intl.DateTimeFormat().resolvedOptions().timeZone" always returns a cached value.

Steps to reproduce the problem:

1. Start Microsoft Edge on Window 10 machine
2. Enter Javascript Console by pressing F12 and execute this command:
   Intl.DateTimeFormat().resolvedOptions().timeZone
3. The timezoneId should match the currently set timezone of your system
4. Change your system timezone to another timezone
5. Execute again this command:
   Intl.DateTimeFormat().resolvedOptions().timeZone
6. The timezoneId is still the same from the first call. <= Cached result? Bug?

This procedure works in Chrome without problems. Chrome noticed the changed timezone. So Microsoft has a bug or a "cache feature" ;-) in his Intl.DateTimeFormat() implementation. And because moment-timezone uses this Intl Feature, the moment.tz.guess(true) method also returns the wrong timezone in my cordova app (Edge Browser Engine).

If I remove the Intl Feature at the beginning by doing:
Intl.DateTimeFormat = undefined;

then moment-timezone always guesses the correct timezoneId in my win 10 cordova app.

[mattjohnsonpint]

I'm not concerned about the cached part. Various browsers have gone either way on that over the years. If you're concerned about that, raise an issue with Edge / ChakraCore.

I do think it would be good to make sure Intl returned a zone with a / char in it (or UTC) before accepting the results. Note, jsTimeZoneDetect had a similar issue.

For now, you could simply remove (or don't add) the zones that use three-letter abbreviations instead of full identifiers.

[mattjohnsonpint]

To clarify - a true/false option isn't very useful IMHO, but ignoring bad results is.