Temporal: Month names are missing #64176

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1. Renegade334 commented on Jun 27, 2026

   

   Renegade334

   on Jun 27, 2026

   Last edited by Renegade334

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   Technically a duplicate of #63041.

   There is standards discussion ongoing regarding what the behaviour should be here, as the DateTimeFormat operation is being run with the PlainYearMonth default calendar iso8601, and it's unclear what that means from a DateTimeFormat perspective.
2. Daniel15 commented on Jun 27, 2026

   

   Daniel15

   on Jun 27, 2026

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   Thanks @Renegade334 - sorry I didn't find that issue during my initial search. Do Firefox and Chrome use a different version of the spec, or is this currently undefined behaviour?

   I can confirm that using gregory instead of iso8601 works (... shouldn't it be gregorian, not gregory?)

   > Temporal.PlainYearMonth.from({year: 2026, month: 6, calendar: 'gregory'}).toLocaleString('en-US', {month: 'long', year: 'numeric'})
   'June 2026'
   
3. Daniel15 commented on Jun 27, 2026

   

   Daniel15

   on Jun 27, 2026

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   Actually, I hit a different issue when using the gregory calendar: subtract isn't implemented.

   > Temporal.PlainDate.from({calendar: 'gregory', day: 27, month: 2, year: 2026}).subtract({days: 1})
   Uncaught RangeError: Temporal error: Not yet implemented.
       at PlainYearMonth.subtract (<anonymous>)
   

   I thought this was because there's no timezone, but converting to ZonedDateTime doesn't work either:

   > Temporal.PlainDate.from({calendar: 'gregory', day: 27, month: 2, year: 2026}).toZonedDateTime('America/Los_Angeles').subtract({days: 2})
   Uncaught RangeError: Temporal error: Not yet implemented.
       at ZonedDateTime.subtract (<anonymous>)
   

   This does work properly in the polyfill, so I'll switch to using that until the Node.js implementation is more complete.

   👍React with 👍1Reacted by René
4. Renegade334 commented on Jun 28, 2026

   

   Renegade334

   on Jun 28, 2026

   Last edited by Renegade334

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   Do Firefox and Chrome use a different version of the spec, or is this currently undefined behaviour?

   The spec doesn't currently define any specific behaviour for ca=iso8601. V8 just hands off the formatting to the Unicode library, which is now returning empty strings for non-numeric month/era rather than aliasing to Gregorian.

   Actually, I hit a different issue when using the gregory calendar: subtract isn't implemented.

   Yup, we need to upgrade the Temporal implementation; we are currently using the one that shipped with Chromium 142, which is still a bit rough round the edges.
5. Renegade334

   added

   duplicateIssues and PRs that are duplicates of other issues or PRs.Issues and PRs that are duplicates of other issues or PRs.

   on Jun 28, 2026
6. Renegade334

   closed this as a duplicateof Missing month in Intl.DateTimeFormat output when using calendar: 'iso8601' in Node v24.13.0 and later #63041 on Jun 28, 2026