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, 3 insertions, 2 deletions

diff --git a/test/parallel/test-worker-message-port.js b/test/parallel/test-worker-message-port.js
index 47a8ddf665..dce9da0b30 100644
--- a/test/parallel/test-worker-message-port.js
+++ b/test/parallel/test-worker-message-port.js
@@ -21,14 +21,15 @@ const { MessageChannel, MessagePort } = require('worker_threads');
   const { port1, port2 } = new MessageChannel();
 
   port1.onmessage = common.mustCall((message) => {
-    assert.strictEqual(message, 4);
+    assert.strictEqual(message.data, 4);
+    assert.strictEqual(message.target, port1);
     port2.close(common.mustCall());
   });
 
   port1.postMessage(2);
 
   port2.onmessage = common.mustCall((message) => {
-    port2.postMessage(message * 2);
+    port2.postMessage(message.data * 2);
   });
 }