utcToZonedTime() incorrect while toDate() correct around daylight saving time

[soetji]

This year for "America/New_York" the daylight saving ended on Nov 3, 02:00 where it turned back 01:00. My browser is on a local "America/New_York" system.

toDate() gets this correctly but not utcToZonedTime(). utcToZonedTime() adds an hour even before 02:00.

toDate('2019-11-03T03:00:00.000Z', { timeZone: 'America/New_York' })
// Sat Nov 02 2019 23:00:00 GMT-0400 (Eastern Daylight Time)

utcToZonedTime('2019-11-03T03:00:00.000Z', 'America/New_York')
// Sun Nov 03 2019 00:00:00 GMT-0400 (Eastern Daylight Time)


toDate('2019-11-03T04:00:00.000Z', { timeZone: 'America/New_York' })
// Sun Nov 03 2019 00:00:00 GMT-0400 (Eastern Daylight Time)

utcToZonedTime('2019-11-03T04:00:00.000Z', 'America/New_York')
// Sun Nov 03 2019 01:00:00 GMT-0400 (Eastern Daylight Time)


toDate('2019-11-03T05:00:00.000Z', { timeZone: 'America/New_York' })
// Sun Nov 03 2019 01:00:00 GMT-0400 (Eastern Daylight Time)

utcToZonedTime('2019-11-03T05:00:00.000Z', 'America/New_York')
// Sun Nov 03 2019 01:00:00 GMT-0500 (Eastern Standard Time)


toDate('2019-11-03T06:00:00.000Z', { timeZone: 'America/New_York' })
// Sun Nov 03 2019 01:00:00 GMT-0500 (Eastern Standard Time)

utcToZonedTime('2019-11-03T06:00:00.000Z', 'America/New_York')
// Sun Nov 03 2019 01:00:00 GMT-0500 (Eastern Standard Time)


toDate('2019-11-03T07:00:00.000Z', { timeZone: 'America/New_York' })
// Sun Nov 03 2019 02:00:00 GMT-0500 (Eastern Standard Time)

utcToZonedTime('2019-11-03T07:00:00.000Z', 'America/New_York')
// Sun Nov 03 2019 02:00:00 GMT-0500 (Eastern Standard Time)

[soetji]

It looks like the bug in utcToZonedTime goes with the system timezone. It works correctly on the GMT timezone system.

// Correct on a GMT timezone system
utcToZonedTime('2019-11-03T03:00:00.000Z', 'America/New_York')
// Sat Nov 02 2019 23:00:00 GMT-0400 (Eastern Daylight Time)
utcToZonedTime('2019-11-03T03:00:00.000Z', 'America/New_York').getTimezoneOffset()
// 0

// Incorrect on a America/New_York timezone system
utcToZonedTime('2019-11-03T03:00:00.000Z', 'America/New_York')
// Sun Nov 03 2019 00:00:00 GMT-0400 (Eastern Daylight Time)
utcToZonedTime('2019-11-03T03:00:00.000Z', 'America/New_York').getTimezoneOffset()
// 240

[marnusw]

That's good to know! I'm on GMT so would probably not have managed to reproduce this.

[constgen]

This is a real problem. utcToZonedTime() gives a different result when you use the system timeZone explicitly and pass the date near the DST switching hour

let timeZone = new Intl.DateTimeFormat().resolvedOptions().timeZone
let date = new Date() // choose the date +1h right after switching to Standart Time from Summer Time
let zonedDate = utcToZonedTime(value, timeZone);
let time = format(zonedDate, 'p', { timeZone })
console.log(time) // As the time zone is system, the time should match to `date` time, but it is not.

Actually this formatting produces the same hour 3 times during moving from Summer Time to Standart Time

[altodoro]

Seems like the similar issue here: utcToZonedTime() adds an extra day to the returned date when converting date with time in range 23:00 - 23:59

utcToZonedTime('2020-02-26T23:15:00Z', 'Europe/Berlin');
// expected -> Fri Feb 27 2020 00:15:00 GMT+0200 (Eastern European Standard Time)
// actual   -> Fri Feb 28 2020 00:15:00 GMT+0200 (Eastern European Standard Time)

[marnusw]

@altodoro I think the issue you are reporting is #38 / #43 rather than related to issues around the DST change. Please check whether version 1.0.10 solves your issue.

[altodoro]

@altodoro I think the issue you are reporting is #38 / #43 rather than related to issues around the DST change. Please check whether version 1.0.10 solves your issue.

yep, you're right. Thanks for the update!

[marnusw]

This might be fixed in version 1.0.11 which will be available soon. Please reopen if not.