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Teach ExtendableMessageEvent to work with origins. #1821

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yoshisatoyanagisawa merged 3 commits into from
Mar 12, 2026
Merged

Teach ExtendableMessageEvent to work with origins. #1821

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c92ea02
Teach ExtendableMessageEvent to work with origins.
mikewest Mar 10, 2026
c9e7a59
fixup origin is exported now
mikewest Mar 10, 2026
c890bb1
fixup extract an origin
mikewest Mar 11, 2026
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26 changes: 19 additions & 7 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,8 @@ spec: html; urlPrefix: https://html.spec.whatwg.org/multipage/
urlPrefix: interaction.html
text: visibilityState; for: Document; url: page-visibility
type: dfn
urlPrefix: comms.html
text: concept-MessageEvent-origin; url: concept-messageevent-origin

@annevk annevk Mar 10, 2026

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We should probably export this.

@mikewest mikewest Mar 10, 2026

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I didn't expect anyone outside HTML would need it. Silly me. I'll send you a PR in a minute to add the attribute.

@mikewest mikewest Mar 10, 2026

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Ah. Actually we did export it. I guess it just hasn't landed in the references DB yet. We should be able to drop this ~tomorrow.

urlPrefix: syntax.html
text: delay the load event; for: document; url: delay-the-load-event
urlPrefix: browsers.html
Expand Down Expand Up @@ -515,15 +517,15 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
<dt>Otherwise</dt>
<dd>a new {{Client}} object that represents |incumbentGlobal|'s associated worker</dd>
</dl>
1. Let |origin| be the [=serialization of an origin|serialization=] of |incumbentSettings|'s [=environment settings object/origin=].
1. Let |origin| be |incumbentSettings|'s [=environment settings object/origin=].
1. Let |destination| be the {{ServiceWorkerGlobalScope}} object associated with |serviceWorker|.
1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=global object/Realm=]).

If this throws an exception, let |e| be the result of [=creating an event=] named {{ServiceWorkerGlobalScope/messageerror!!event}}, using {{ExtendableMessageEvent}}, with the {{ExtendableMessageEvent/origin}} attribute initialized to |origin| and the {{ExtendableMessageEvent/source}} attribute initialized to |source|.
If this throws an exception, let |e| be the result of [=creating an event=] named {{ServiceWorkerGlobalScope/messageerror!!event}}, using {{ExtendableMessageEvent}}, with its [=ExtendableMessageEvent/origin=] initialized to |origin| and the {{ExtendableMessageEvent/source}} attribute initialized to |source|.
1. Else:
1. Let |messageClone| be |deserializeRecord|.\[[Deserialized]].
1. Let |newPorts| be a new [=frozen array type|frozen array=] consisting of all {{MessagePort}} objects in |deserializeRecord|.\[[TransferredValues]], if any, maintaining their relative order.
1. Let |e| be the result of [=creating an event=] named {{ServiceWorkerGlobalScope/message!!event}}, using {{ExtendableMessageEvent}}, with the {{ExtendableMessageEvent/origin}} attribute initialized to |origin|, the {{ExtendableMessageEvent/source}} attribute initialized to |source|, the {{ExtendableMessageEvent/data}} attribute initialized to |messageClone|, and the {{ExtendableMessageEvent/ports}} attribute initialized to |newPorts|.
1. Let |e| be the result of [=creating an event=] named {{ServiceWorkerGlobalScope/message!!event}}, using {{ExtendableMessageEvent}}, with its [=ExtendableMessageEvent/origin=] initialized to |origin|, the {{ExtendableMessageEvent/source}} attribute initialized to |source|, the {{ExtendableMessageEvent/data}} attribute initialized to |messageClone|, and the {{ExtendableMessageEvent/ports}} attribute initialized to |newPorts|.
1. [=Dispatch=] |e| at |destination|.
1. Invoke [=Update Service Worker Extended Events Set=] with |serviceWorker| and |e|.
</section>
Expand Down Expand Up @@ -1276,14 +1278,14 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
1. If |targetClient| is null, return.
1. Let |destination| be the {{ServiceWorkerContainer}} object whose associated [=ServiceWorkerContainer/service worker client=] is |targetClient|.
1. Add a [=task=] that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
1. Let |origin| be the [=serialization of an origin|serialization=] of |sourceSettings|'s [=environment settings object/origin=].
1. Let |origin| be |sourceSettings|'s [=environment settings object/origin=].
1. Let |source| be the result of [=getting the service worker object=] that represents |contextObject|'s [=relevant global object=]'s [=ServiceWorkerGlobalScope/service worker=] in |targetClient|.
1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=relevant Realm=]).

If this throws an exception, catch it, [=fire an event=] named {{ServiceWorkerContainer/messageerror!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin| and the {{MessageEvent/source}} attribute initialized to |source|, and then abort these steps.
If this throws an exception, catch it, [=fire an event=] named {{ServiceWorkerContainer/messageerror!!event}} at |destination|, using {{MessageEvent}}, with its [=concept-MessageEvent-origin|origin=] initialized to |origin| and the {{MessageEvent/source}} attribute initialized to |source|, and then abort these steps.
1. Let |messageClone| be |deserializeRecord|.\[[Deserialized]].
1. Let |newPorts| be a new [=frozen array type|frozen array=] consisting of all {{MessagePort}} objects in |deserializeRecord|.\[[TransferredValues]], if any.
1. [=Dispatch|Dispatch an event=] named {{Window/message!!event}} at |destination|, using {{MessageEvent}}, with the {{MessageEvent/origin}} attribute initialized to |origin|, the {{MessageEvent/source}} attribute initialized to |source|, the {{MessageEvent/data}} attribute initialized to |messageClone|, and the {{MessageEvent/ports}} attribute initialized to |newPorts|.
1. [=Dispatch|Dispatch an event=] named {{Window/message!!event}} at |destination|, using {{MessageEvent}}, with its [=concept-MessageEvent-origin|origin=] initialized to |origin|, the {{MessageEvent/source}} attribute initialized to |source|, the {{MessageEvent/data}} attribute initialized to |messageClone|, and the {{MessageEvent/ports}} attribute initialized to |newPorts|.
</section>

<section>
Expand Down Expand Up @@ -1819,6 +1821,8 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
};
</pre>

Each {{ExtendableMessageEvent}} has an <dfn for="ExtendableMessageEvent">origin</dfn> (an [=/origin=], a string, or null), initially null.

[=/Service workers=] define the <a method lt="waitUntil()" for="ExtendableEvent">extendable</a> {{ServiceWorkerGlobalScope/message!!event}} event to allow extending the lifetime of the event. For the {{ServiceWorkerGlobalScope/message!!event}} event, [=/service workers=] use the {{ExtendableMessageEvent}} interface which extends the {{ExtendableEvent}} interface.

<section>
Expand All @@ -1830,7 +1834,15 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
<section>
<h4 id="extendablemessage-event-origin">{{ExtendableMessageEvent/origin|event.origin}}</h4>

The <dfn attribute for="ExtendableMessageEvent">origin</dfn> attribute *must* return the value it was initialized to. When the object is created, this attribute *must* be initialized to the empty string. It represents the [=environment settings object/origin=] of the [=/service worker client=] that sent the message.
The <dfn attribute for="ExtendableMessageEvent">origin</dfn> attribute represents the [=environment settings object/origin=] of the [=/service worker client=] that sent the message.

The {{ExtendableMessageEvent/origin}} getter steps are:

1. If [=this=]'s [=ExtendableMessageEvent/origin=] is an [=/origin=], then return the [=serialization of an origin|serialization=] of [=this=]'s [=ExtendableMessageEvent/origin=].
1. If [=this=]'s [=ExtendableMessageEvent/origin=] is null, then return the empty string.
1. Return [=this=]'s [=ExtendableMessageEvent/origin=].

When the {{ExtendableMessageEvent/origin}} attribute is "initialized" (during {{ExtendableMessageEvent}}'s constructor, for example), the initialization value is placed into the object's [=ExtendableMessageEvent/origin=].
</section>

<section>
Expand Down