[Behind Pref] [Web API] Implement worker modules

[Rumyra]

Acceptance Criteria

• The listed features are documented sufficiently on MDN
• BCD is updated
• Interactive example and data repos are updated if appropriate
• The content has been reviewed as needed

For folks helping with Firefox related documentation

• Set bugs to dev-doc-complete
• Add entry to Firefox release notes if feature is enabled in release
• Add entry to Firefox experimental features page if feature is not yet enabled in release

Features to document

We have a few things dotted about about this, so not sure if there's much else to document. Rel note & bcd as per

Related Gecko bugs

https://bugzilla.mozilla.org/show_bug.cgi?id=1247687
https://bugzilla.mozilla.org/show_bug.cgi?id=1812628 - Behind pref

Other

• Check content open issues to see if any pertain to the subject matter. If there are any that can be closed because of the work, do so. If there are any that can be fixed relatively quickly because of the knowledge from completing this issue and you have time, feel free to go ahead and fix them.
• Check if glossary updates are required for the feature you're documenting - whether an existing term needs to be updated or a new term should be added.
• Check if BCD update means that content pages need to have experimental markup removed or deprecated markup added (front matter tags and macros).

[hamishwillee]

Status:

This is behind pref and in nightly. Only supported for import (static import) not import() (dynamic import).

• Release notes - FF111 Exper Feature: Implement worker modules #25030
• BCD
  • Ff111 implements workers modules browser-compat-data#19044
  • Add compatibility note about Safari's support for nested workers browser-compat-data#19045 - tidy up
  • FF does not support dynamic module import in workers browser-compat-data#19054
• Docs - basically OK, but maybe a little cleanup.
  • Remove note about nested workers/webkit in Worker - Remove note about nested workers not supported in Safari #25209
  • Service workers cannot do dynamic import #25283
  • Remove note about data: urls at start of Worker() - following up in Worker data: url is opaque cross origin right? whatwg/html#8986 [IF don't get response, just drop this]
• dev-doc-complete

The core work for release is done - that was just BCD and experimental features.

Still doing some cleanup though for old info in the pages that should be in BCD. If any of this can't go through it wouldn't be tragic if it was dropped.

[hamishwillee]

Closing. Core work done. I'll keep an eye on the clean up item, but not hopeful I'll get a clear answer from anyone.

[okikio]

Does Firefox support module workers now? I thought it would be announced in the Firefox 111 announcement but it wasn't

[WolfgangDrescher]

Yes it does, but you have to enable it manually via about:config and set dom.workers.modules.enabled to true.

https://caniuse.com/mdn-api_worker_worker_ecmascript_modules

I wonder when it will be enabled by default.

[okikio]

Thanks 👍🏽

[hamishwillee]

I wonder when it will be enabled by default.

Probably not long. Support for dynamic import of modules into workers was just added (behind pref - I htink in 113). I think the goal was to release this when support for both was available, so probably after a release (or two) of hardening.

[okikio]

Awesome 👌

[adamziel]

This only covers web workers, not service workers, right? WordPress Playground builds its service worker to an ES Module in local development mode, and that doesn't work on Firefox. The production build produces a regular JavaScript file and works without issues.

[hamishwillee]

@adamziel At the time I wrote this static/dynamic import was planned for shared/dedicated workers, along with static import of modules in service workers (and as I recall full support for the spec came in FF114).

The spec authors weren't sure what to do with dynamic import into service workers, as per w3c/ServiceWorker#1585. This might have changed - I'm not tracking it.

[adamziel]

@hamishwillee oh, I meant service workers with type: 'module', not dynamic imports specifically:

	await navigator.serviceWorker.register(scriptUrl, {
		type: 'module',
	});

[hamishwillee]

You mean "does firefox support service workers of type "module"? Probably not.

I base this on https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerContainer/register#module which says

'module'
The loaded service worker is in an ES module and the import statement is available on worker contexts. For ES module compatibility info, see the browser compatibility data table for the ServiceWorker interface.

If you look at browser compatibility data table for the ServiceWorker interface. it says FF service workers do not have "Support for ECMAScript modules"