`Symbol.toStringTag` on `MessageChannel` and `MessagePort`

[brettz9]

Version

v26.7.0

Platform

Darwin MacBook-Air-3.local 25.5.0 Darwin Kernel Version 25.5.0: Tue Jun  9 22:26:46 PDT 2026; root:xnu-12377.121.10~1/RELEASE_ARM64_T8103 arm64

Subsystem

No response

What steps will reproduce the bug?

node -e "console.log(Object.prototype.toString.call(new MessageChannel()))"

node -e "console.log(Object.prototype.toString.call(new MessageChannel().port1))"

How often does it reproduce? Is there a required condition?

Always. No special required condition.

What is the expected behavior? Why is that the expected behavior?

Display [object MessageChannel] and [object MessagePort] respectively.

What do you see instead?

[object Object]

[object EventTarget]

Additional information

No response

[santusht06]

Root Cause Analysis

1. MessagePort & BroadcastChannel: Both classes set their prototypes to inherit from NodeEventTarget.prototype via ObjectSetPrototypeOf(MessagePort.prototype, NodeEventTarget.prototype). Because neither class defined their own [Symbol.toStringTag], they inherited the value from EventTarget.prototype[Symbol.toStringTag] ('EventTarget'), causing Object.prototype.toString.call(port) to evaluate to [object EventTarget].
2. MessageChannel: MessageChannel did not define Symbol.toStringTag on its prototype, falling back to Object.prototype ([object Object]).

Solution

In lib/internal/worker/io.js, we define [SymbolToStringTag] on MessagePort.prototype, MessageChannel.prototype, and BroadcastChannel.prototype with { configurable: true, writable: false, enumerable: false, value: <InterfaceName> } per WebIDL specifications.

A fix with full test coverage has been submitted in PR #65531.