undici: The "event" argument must be an instance of Event. Received an instance of Event (WebSocket + ws)

Bug Description

When Undici calls fireEvent with the MessageEvent received from the server constructed via the ws package, the following error is thrown by internals/event_target:

The "event" argument must be an instance of Event. Received an instance of Event

Reproducible By

import { WebSocketServer } from 'ws'
import { WebSocket } from 'undici'

const server = new WebSocketServer({ host: '127.0.0.1', port: 0 })
server.on('connection', (client) => {
  client.on('message', (data) => {
    client.send('greetings')
  })
})

const ws = new WebSocket(server.address())
ws.addEventListener('open', () => {
  ws.send('hello')
})
ws.addEventListener('message', (event) => {
  ws.send('client received:', event.data)
})

Expected Behavior

The MessageEvent dispatched via fireEvent does not throw an error.

Logs & Screenshots

Environment

os: MacOS 14.2.1 (23C71)
node: v18.17.0

Additional context

Here’s the check that Node performs before throwing that error:

https://github.com/nodejs/node/blob/64c6d97463c29bade4d6081683dab2cd7cda298d/lib/internal/event_target.js#L751

I suspect that the MessageEvent provided by the ws package doesn’t extend the global Event correctly, and thus fails the instanceof check. I still think it’s worth opening the issue in Undici for discoverability even if the root cause will end up to be elsewhere.