worker: use fake MessageEvent for port.onmessage

Instead of passing the payload for Workers directly to `.onmessage`,
perform something more similar to what the browser API provides,
namely create an event object with a `.data` property.

This does not make `MessagePort` implement the `EventTarget` API, nor
does it implement the full `MessageEvent` API, but it would make
such extensions non-breaking changes if we desire them at
some point in the future.

(This would be a breaking change if Workers were not experimental.
Currently, this method is also undocumented and only exists with
the idea of enabling some degree of Web compatibility.)

PR-URL: https://github.com/nodejs/node/pull/26082
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/lib/internal/worker/io.js b/lib/internal/worker/io.js
index 9aa8c19958..a72868916c 100644
--- a/lib/internal/worker/io.js
+++ b/lib/internal/worker/io.js
@@ -61,11 +61,11 @@ MessagePort.prototype.unref = MessagePortPrototype.unref;
 // uv_async_t) which can receive information from other threads and emits
 // .onmessage events, and a function used for sending data to a MessagePort
 // in some other thread.
-MessagePort.prototype[kOnMessageListener] = function onmessage(payload) {
-  if (payload.type !== messageTypes.STDIO_WANTS_MORE_DATA)
-    debug(`[${threadId}] received message`, payload);
+MessagePort.prototype[kOnMessageListener] = function onmessage(event) {
+  if (event.data && event.data.type !== messageTypes.STDIO_WANTS_MORE_DATA)
+    debug(`[${threadId}] received message`, event);
   // Emit the deserialized object to userland.
-  this.emit('message', payload);
+  this.emit('message', event.data);
 };
 
 // This is for compatibility with the Web's MessagePort API. It makes sense to