worker: expose sender on BroadcastChannel MessageEvent

Author: SudhansuBandha

doc/api/worker_threads.md

@@ -995,6 +995,65 @@ added: v15.4.0
 
 * `message` {any} Any cloneable JavaScript value.
 
+### `messageEvent.sender`
+
+<!-- YAML added: REPLACEME -->
+
+> Stability: 1 - Experimental
+
+Type: {number}
+
+A Node.js-specific extension that identifies the sender of a
+BroadcastChannel message.
+
+When a message originates, sender is the threadId of the
+worker that posted the message.
+
+```mjs
+import {
+  isMainThread,
+  BroadcastChannel,
+  Worker,
+} from 'node:worker_threads';
+
+const bc = new BroadcastChannel('hello');
+
+if (isMainThread) {
+  let c = 0;
+  bc.onmessage = ({ data, sender }) => {
+    console.log(`Received "${data}" from worker ${sender}`);
+    if (++c === 10) bc.close();
+  };
+  for (let n = 0; n < 10; n++)
+    new Worker(new URL(import.meta.url));
+} else {
+  bc.postMessage('hello from every worker');
+  bc.close();
+}
+```
+
+```cjs
+const {
+  isMainThread,
+  BroadcastChannel,
+  Worker,
+} = require('node:worker_threads');
+
+const bc = new BroadcastChannel('hello');
+
+if (isMainThread) {
+  let c = 0;
+  bc.onmessage = ({ data, sender }) => {
+    console.log(`Received "${data}" from worker ${sender}`);
+    if (++c === 10) bc.close();
+  };
+  for (let n = 0; n < 10; n++)
+    new Worker(__filename);
+} else {
+  bc.postMessage('hello from every worker');
+  bc.close();
+}
+```
 ### `broadcastChannel.ref()`
 
 <!-- YAML

lib/internal/worker/io.js

@@ -347,7 +347,15 @@ function receiveMessageOnPort(port) {
 }
 
 function onMessageEvent(type, data) {
-  this.dispatchEvent(lazyMessageEvent(type, { data: data.value, source: data.source }));
+  const event = lazyMessageEvent(type, { data: data.value });
+  ObjectDefineProperty(event, 'sender', {
+    __proto__: null,
+    value: data.sender,
+    enumerable: false,
+    writable: false,
+    configurable: false,
+  });
+  this.dispatchEvent(event);
 }
 
 function isBroadcastChannel(value) {
@@ -421,7 +429,7 @@ class BroadcastChannel extends EventTarget {
    */
   postMessage(message) {
     const broadcastMessage = {
-      source: threadId,
+      sender: threadId,
       value: message,
     };
     if (!isBroadcastChannel(this))

test/parallel/test-worker-broadcastchannel.js

@@ -195,7 +195,7 @@ assert.throws(() => new BroadcastChannel(), {
 
     bc.onmessage = (evt) => {
       assert.strictEqual(evt.data, 'from-main');
-      assert.strictEqual(evt.source, 0);
+      assert.strictEqual(evt.sender, 0);
 
       bc.close();
     };
@@ -206,7 +206,7 @@ assert.throws(() => new BroadcastChannel(), {
   bc.onmessage = common.mustCall((evt) => {
     assert.strictEqual(evt.data, 'from-worker');
 
-    assert.ok(evt.source > 0);
+    assert.ok(evt.sender > 0);
 
     bc.postMessage('from-main');
     bc.close();