I've searched the internet for a quick demo/tutorial of WebRTC that teached me to send a text from one computer to another. Couldn't find anything small and simple enough and still usable. Wrote this: https://gist.github.com/fiatjaf/229a5db2f431ab707e3fb909240d..., it may be worth of your reading.

We just wrote a very detailed step-by-step article on getting started with WebRTC data channels using TDD: https://medium.com/@coldbrewtesting/getting-started-with-web...

It was more an experiment in creating a fully serverless game contained in client side JS. Even the matchmaking is client side, however I believe PeerJS does use a server to broker conmections.