There are two dirs: 'backend' and 'frontend'. From backend folder run:
npm i
node .
Then open in browser 'index.html' from 'frontend' folder and login, using the cred-data written on the newly opened page. You can open many browsers / tabs and chat :)
There is also a server bot in the chat that periodically sends messages.
Backend uses wonderful 0-dependencies ws package, that implements websocket protocol.