worker: define Symbol.toStringTag on messaging prototypes

lib/internal/worker/io.js

@@ -15,6 +15,7 @@ const {
   ReflectApply,
   Symbol,
   SymbolFor,
+  SymbolToStringTag,
 } = primordials;
 
 const {
@@ -208,6 +209,19 @@ ObjectDefineProperty(MessagePort.prototype, inspect.custom, {
   },
 });
 
+ObjectDefineProperty(MessagePort.prototype, SymbolToStringTag, {
+  __proto__: null,
+  configurable: true,
+  value: 'MessagePort',
+});
+
+ObjectDefineProperty(MessageChannel.prototype, SymbolToStringTag, {
+  __proto__: null,
+  configurable: true,
+  value: 'MessageChannel',
+});
+
+
 function setupPortReferencing(port, eventEmitter, eventName) {
   // Keep track of whether there are any workerMessage listeners:
   // If there are some, ref() the channel so it keeps the event loop alive.
@@ -464,6 +478,11 @@ ObjectDefineProperties(BroadcastChannel.prototype, {
   name: kEnumerableProperty,
   close: kEnumerableProperty,
   postMessage: kEnumerableProperty,
+  [SymbolToStringTag]: {
+    __proto__: null,
+    configurable: true,
+    value: 'BroadcastChannel',
+  },
 });
 
 defineEventHandler(BroadcastChannel.prototype, 'message');

test/parallel/test-eventtarget-memoryleakwarning.js

@@ -15,12 +15,12 @@ common.expectWarning({
         'EventTarget. MaxListeners is 2. Use events.setMaxListeners() ' +
      'to increase limit'],
     ['Possible EventTarget memory leak detected. 3 foo listeners added to ' +
-        '[MessagePort [EventTarget]]. ' +
+        '[MessagePort]. ' +
         'MaxListeners is 2. ' +
         'Use events.setMaxListeners() to increase ' +
      'limit'],
     ['Possible EventTarget memory leak detected. 3 foo listeners added to ' +
-        '[MessagePort [EventTarget]]. ' +
+        '[MessagePort]. ' +
         'MaxListeners is 2. ' +
         'Use events.setMaxListeners() to increase ' +
      'limit'],

test/parallel/test-worker-message-port-inspect-during-init-hook.js

@@ -12,7 +12,7 @@ async_hooks.createHook({
   init: common.mustCall((id, type, triggerId, resource) => {
     assert.strictEqual(
       util.inspect(resource),
-      'MessagePort [EventTarget] { active: true, refed: false }');
+      'MessagePort { active: true, refed: false }');
   }, 2)
 }).enable();
 

test/parallel/test-worker-messaging-string-tag.js

@@ -0,0 +1,38 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { MessageChannel, MessagePort, BroadcastChannel } = require('worker_threads');
+
+const classesToBeTested = [
+  MessageChannel,
+  MessagePort,
+  BroadcastChannel,
+];
+
+for (const cls of classesToBeTested) {
+  assert.strictEqual(cls.prototype[Symbol.toStringTag], cls.name);
+  assert.deepStrictEqual(
+    Object.getOwnPropertyDescriptor(cls.prototype, Symbol.toStringTag),
+    { configurable: true, enumerable: false, value: cls.name, writable: false }
+  );
+}
+
+const channel = new MessageChannel();
+assert.strictEqual(Object.prototype.toString.call(channel), '[object MessageChannel]');
+assert.strictEqual(Object.prototype.toString.call(channel.port1), '[object MessagePort]');
+assert.strictEqual(Object.prototype.toString.call(channel.port2), '[object MessagePort]');
+
+const broadcast = new BroadcastChannel('test');
+assert.strictEqual(Object.prototype.toString.call(broadcast), '[object BroadcastChannel]');
+broadcast.close();
+
+// Test globals
+assert.strictEqual(globalThis.MessageChannel, MessageChannel);
+assert.strictEqual(globalThis.MessagePort, MessagePort);
+assert.strictEqual(globalThis.BroadcastChannel, BroadcastChannel);
+assert.strictEqual(Object.prototype.toString.call(new globalThis.MessageChannel()), '[object MessageChannel]');
+assert.strictEqual(Object.prototype.toString.call(new globalThis.MessageChannel().port1), '[object MessagePort]');
+const globalBroadcast = new globalThis.BroadcastChannel('test-global');
+assert.strictEqual(Object.prototype.toString.call(globalBroadcast), '[object BroadcastChannel]');
+globalBroadcast.close();