Interop 2025 announced

Interop 2025 is a cross-browser effort to improve the interoperability of the web — to reach a state where each technology works exactly the same in every browser.

[https://wpt.fyi/interop-2025]

Resources:

• https://github.com/web-platform-tests/interop
• https://github.com/web-platform-tests/interop/tree/main/2025
• https://wpt.fyi/interop-2025

Announcements by contributors:

• https://hacks.mozilla.org/2025/02/interop-2025/
• https://web.dev/blog/interop-2025
• https://webkit.org/blog/16458/announcing-interop-2025/
• https://blogs.windows.com/msedgedev/2025/02/13/microsoft-edge-and-interop-2025/
• https://www.igalia.com/2025/02/13/Interop-2025.html
• https://www.bocoup.com/blog/interop-2025

ECMAScript Temporal may soon land in Browsers

Temporal is an ECMAScript proposal to add new date and time APIs to JavaScript.

• https://github.com/tc39/proposal-temporal
• https://linkedlist.ch/javascript_temporal_40/

It has been in the making for a long time by now. The proposal's repository appeared in 2017 and a lot of activity happened within the last four years. One topic that took a while was the IETF standardization of string formats used in zone annotations. But that has been completed at the end of 2023.

In mid 2024, a scope reduction was discussed at the meetings of TC39. Apparently, some implementors have reservations about the proposal's size and complexity. As a result, some parts of the proposal were removed and may be added in future proposals instead.

But now, finally, it looks like we may soon see Temporal within browsers and other JavaScript engines. Until recently, implementors were not allowed to ship Temporal implementations without hiding them behind a flag. But that restriction was removed from Temporal's README in January. And in the July meeting of TC39, it was noted that Temporal implementations may ship unflagged. Even better, the work-in-progress implementations of Temporal in SpiderMonkey (Firefox), V8 (Chrome), and JavaScriptCore (Safari) already pass many of the required feature tests.

• https://github.com/tc39/notes/pull/337
• https://github.com/tc39/notes/blob/c7ba9a7eb7ce502cdba1ff0d86581e84e1d4405f/meetings/2024-07/july-30.md#temporal-update--bug-fixes

One remaining open issue is the final normative specification text for ECMAScript Temporal, though. But we may already see first implementations and polyfills hopefully soon. Thanks to everybody involved in the process!

Temporal: Scope Reduction

The meeting of Ecma TC39 in June 2024 discussed the Temporal proposal that has been in the works for a long time by now. Unfortunately, the discussion was not about being able to publish it soon. Instead, a scope reduction was proposed. Apparently, implementors (Google, Apple, Mozilla) have reservations about the proposal's scope size and complexity.

• https://github.com/tc39/proposal-temporal
• https://github.com/tc39/agendas/blob/main/2024/06.md#agenda-items
• https://docs.google.com/presentation/d/1PPMAxVnVjFwRPuJwOvVsw9nZLQ6jDM8Hd5PNO0Grp4I/edit#slide=id.p

Further information and the exact discussions that took place presumably were not publicly available so far. But now, there is an open PR to add these to the usual repository that contains TC39 meeting notes.

• https://github.com/tc39/notes/pull/330
• https://github.com/tc39/notes/blob/e9e203a8389a2300573209cee58bb1457bc72b07/meetings/2024-06/june-12.md#temporal-stage-3-update-and-scope-reduction

Conclusion: The committee reached consensus that the Temporal proposal is apparently too big. Some parts of it need to be stripped for now and may be reconsidered in follow-up proposals. Specifically, the following parts will be removed from the current proposal:

• Temporal.Calendar
• user calendars
• Temporal.TimeZone
• user time zones
• getISOFields() methods
• withPlainDate() methods
• PlainTime’s toPlainDateTime and toZonedDateTime methods
• epochSeconds properties
• epochMicroseconds properties
• Instant.fromEpochSeconds
• Instant.fromEpochMicroseconds
• PlainDateTime and ZonedDateTime’s toPlainYearMonth and toPlainMonthDay methods
• Instant’s toZonedDateTime method
• Now.zonedDateTime
• Now.plainDateTime
• Now.plainDate
• relativeTo option from Duration.add.

Let's hope that at least the subset of Temporal can be published as a standard soon. Ideally with ECMAScript 2025.

ECMAScript 2024 published

ECMAScript 2024 has been released.

• https://github.com/tc39/ecma262/releases/tag/es2024
• https://262.ecma-international.org/15.0/
• ECMAScript Links

The following proposals have reached stage 4 and are part of ECMAScript 2024:

• Well-Formed Unicode Strings
  • [MDN] String#isWellFormed()
  • [MDN] String#toWellFormed()
• Atomics.waitAsync
  • [MDN] Atomics.waitAsync()
• RegExp v flag with set notation + properties of strings
  • [MDN] RegExp#unicodeSets
• Resizable and growable ArrayBuffers
  • [MDN] ArrayBuffer
  • [MDN] SharedArrayBuffer
• Array Grouping
  • [MDN] Object.groupBy()
  • [MDN] Map.groupBy()
• Promise.withResolvers
  • [MDN] Promise.withResolvers()
• ArrayBuffer transfer
  • [MDN] ArrayBuffer

Most of these new features have already landed in all the important browser engines.

Vertical Centering with CSS

Vertical centering with CSS has been easy for a couple of years now. Both flexible box layout and grid layout support it. Just use them together with the align-content property.

div {
  display: grid; /* or flex */
  align-content: center;
}

And it is about to become even simpler. The specification of the align-content property was not limited to flexbox and grid layout, but it also included block containers. No browser supported that so far, though. But that is about to change as Firefox 125, Safari 17.4, and Chrome 123 (will) support it. Supporting browsers will vertically center even without defining a display property.

div {
  align-content: center;
}

For backward compatibility (and as feature detecting this particular behaviour is currently not possible in a sensible way), it is still recommended to only use it together with flex or grid for the foreseeable future.