Having some issues when use a timezone with zero offset with locale method

[nkeyy0]

I'm having some issues with parsing timezones with zero offsets.

Issue description

I have unexpected results when applying locale for the dayjs object in UTC and timezone with zero offsets. When I call the locale method after .tz() looks like the locale method is changed date-time according to my local time. But with timezones which is different from UTC, everything works fine.

Code

My plugins

import dayjs from 'dayjs';
import advancedFormat from 'dayjs/plugin/advancedFormat';
import calendar from 'dayjs/plugin/calendar';
import customParseFormat from 'dayjs/plugin/customParseFormat';
import localizedFormat from 'dayjs/plugin/localizedFormat';
import timezone from 'dayjs/plugin/timezone';
import utc from 'dayjs/plugin/utc';

dayjs.extend(advancedFormat);
dayjs.extend(customParseFormat);
dayjs.extend(utc);
dayjs.extend(localizedFormat);
dayjs.extend(timezone);
dayjs.extend(calendar);

I don't import locales here, but I import them dynamically after a user selects a specific locale.

Code with issues

dayjs.utc(date).tz(timeZone).locale(locale).format(localizedFormats[dateFormat])

The date argument in that case is a date string in ISO format. Timezone is the string, locale is the string with one of the dayjs locales. Everything works fine until I pass the timezone with zero offsets. I've tried to test this behavior and found that the issue is probably in the clone method

Logs

Date argument is 2022-02-27T11:05:51.439Z in ISO format

Code

      console.log('only timezone', dayjs.utc(date).tz(timeZone));
      console.log('timezone + locale', dayjs.utc(date).tz(timeZone).locale(locale));
      console.log('clone + timezone', dayjs.utc(date).tz(timeZone).clone());

Results

1. With zero offset
   
2. With non-zero offset
   
   

Expected behavior

The date and time should be the same after locale method call

Information

• Day.js Version: 1.11.7
• OS: Windows 10 (64-bit)
• Browser: Firefox 110.0 (64-bit)
• Time zone: Europe/Warsaw [UTC + 01:00]

[ohsory1324]

+1

@iamkun Do you know this issue?

[dungle1811]

I've got the same problem when I passed in the timezone "UTC":

dayjs.tz("2023-12-06T07:43:14.674Z", "UTC").locale("en").format("LT") returns wrong value 12:43 AM
dayjs.tz("2023-12-06T07:43:14.674Z", "UTC").format("LT") returns the expected value 7:43 AM