BroadcastChannel: onmessage must be null

[bnoordhuis]

Version

No response

Platform

No response

Subsystem

No response

What steps will reproduce the bug?

const { BroadcastChannel } = require('worker_threads')
const c = new BroadcastChannel("x")
if (c.onmessage !== null) throw "fail" // it's undefined

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

No response

What is the expected behavior?

No response

What do you see instead?

Additional information

Rabbit hole: browsers and deno agree .onmessage and .onmessageerror are getters+setters inherited from EventTarget.

[benjamingr]

This is a problem with how we do event handlers - it needs to always return null. I'll open a PR.