When Local Clock set to 12AM hour, Chrome returns incorrect TZ values

Describe the bug Steps:

1. set your local clock time on your machine to the 12AM hour
2. have a script that loads dayjs and extends utc & timezone
3. open firefox and run command in console:
4. open chrome or MS edge and run the same command in console

   dayjs
     .tz(
       dayjs().format('YYYY-MM-DD HH:mm'), // get local date and time
       'America/Los_Angeles'
     )
     .day(2)                               // set it to Tuesday
     .hour(23)                             // set the hour late in the day
     .minute(1)                            // set some random minute
     .tz('America/Chicago')                // now convert it to a tz for the next day (should be wednesday)
     .format(`dddd h:mm A [America/Chicago]`);
   

Expected behavior

• The day should be set to Wednesday when converting, but Chrome is saying it’s Tuesday.
• Issue does not happen outside of the 12:00-12:59AM window

Information

• Day.js Version: 1.8.35
• OS: MacOS Catalina 10.15.6
• Browser:
  • Failing Chrome Based browsers:
    • Chrome 85.0.4183.83
    • MS Edge 85.0.564.44
  • Succeeds in Firefox:
    • Firefox 80.0.1
• Time zone: GMT-07:00 DST (Pacific Daylight Time)

[iamkun]

Yes, I can reproduce this issue after changing my system timezone to GMT-07:00 and time to 12:59 AM (yes, it’s available in this locale)

However, I don’t know why there’s a different result between chrome and firefox.

I’ll mark this as a bug and digging it deeply later.

[beatzball]

although i still think this is a bug, my workaround is that i’ve explicitly defined the time in the beginning to always be 12:00 instead of relying on the local time (which could at some point be between 00:00 and 00:59)

dayjs
  .tz(
    dayjs().format('YYYY-MM-DD [12:00]'), // get local date and force time of 12:00
    'America/Los_Angeles'
  )
  .day(2)                               // set it to Tuesday
  .hour(23)                             // set the hour late in the day
  .minute(1)                            // set some random minute
  .tz('America/Chicago')                // now convert it to a tz for the next day (should be wednesday)
  .format(`dddd h:mm A [America/Chicago]`);