resepct utc when passed to tz #2949
Open
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Xiphoseer
reviewed
Nov 7, 2025
| const hasExplicitOffset = /[Zz]|[+-]\d\d:?(\d\d)?$/.test(input) | ||
| if (hasExplicitOffset) { | ||
| const utcDate = d.utc(input, parseFormat) | ||
| utcDate.$x.$timezone = timezone |
There was a problem hiding this comment.
Doing it this way doesn't set the offset or any of the time fields so the resulting object likely doesn't do what you think it does here. It's also not covered by test cases, your input is UTC (not an offset), toISOString is always UTC, so comparing it to moment will pass with any value for timezone.
iamkun
reviewed
Nov 20, 2025
| return d(input).tz(timezone) | ||
| } | ||
|
|
||
| const hasExplicitOffset = /[Zz]|[+-]\d\d:?(\d\d)?$/.test(input) |
Owner
There was a problem hiding this comment.
const hasTimezoneInfo = /Z|[+-]\d{2}:?\d{2}$/.test(input)
if (hasTimezoneInfo && !parseFormat) {
return d(input).tz(timezone)
}
Can we fix it in this way?
- Detect if the input string has timezone markers (Z or +HH:MM)
- If yes & no custom format: Let dayjs parse it normally (which correctly handles UTC), then convert to target timezone
- If no: Keep existing behavior (treat as local time in target timezone)
Contributor
Author
There was a problem hiding this comment.
Yeah sounds good, will run a few tests
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
When parsing UTC timestamps (e.g. containing Z or +00:00) while a default timezone is set, Day.js currently reapplies the default timezone offset, resulting in incorrect conversions.
This PR updates the timezone plugin to correctly detect UTC input and preserve its UTC value instead of re-offsetting.
Resolves #2946