Twitch Chat at it’s core is just IRC, and you can connect to it using a IRC/websocket library. If you want to do it all yourself and directly use websockets like the chat sample github project you linked then you’ll have to do everything yourself, including handling connection errors, responding to PING events etc… Using a library designed for Twitch chat will take care of most of the behind the scenes stuff for you.
As for tmi.js, it’s very outdated and barely maintained so most users have switched over to using https://github.com/twitch-apis/twitch-js which is a community updated version of the library and is very active.