Wrong timezone for "Europe/Helsinki"

[reinisp]

When PC time is set to "(UTC+02:00) Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius", new Date(4331480400000) and moment(4331480400000).tz('Europe/Helsinki') returns different results.

MomentJs returns 120 offset, but it should be 180.

Issue starts to appear starting from 2038 year.

Expected result moment(4331480400000).tz('Europe/Helsinki').date() returns the same result as new Date(4331480400000) .getDate() .

[mattjohnsonpint]

Sure.

moment(4331480400000).tz('Europe/Helsinki').format() // "2107-04-05T23:00:00+02:00"
moment(4331480400000).format()                       // "2107-04-06T00:00:00+03:00"

This is just too far out into the future.

Windows is assuming today's time zone rule will repeat year over year indefinitely.

Moment-timezone has to project transitions at specific times, for each and every year. We can't go on forever, or our data size would be prohibitively large. We currently stop just before year 2038. Past that, we have no transition data.

var untils = moment.tz.zone('Europe/Helsinki').untils;
untils[untils.length-1]  // Infinity
untils[untils.length-2]  // 2140045200000
moment.tz(2140045200000, 'Europe/Helsinki').format() // "2037-10-25T03:00:00+02:00"

Note that projecting transitions for any date in the future is making the assumption that nothing will change between now and then. The further out you go, the less likely this assumption is to be accurate. Even 2038 is a stretch, but we have to pick something.

Some time zones change with very little notice, so if you are working with future dates, you should be careful to reassess things often. See also: http://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/