How to create private message system in your app?

Since I didn't find a simple JS libs to add PMs to my app which I could easily change and extend I started creating my own and actually found it very useful, and made it more re-usable and configurable.

I am going to publish a new BunnyJS component soon - Bunny Messenger, which will allow to add private message system to any app easily. Just focus on business and your app, add some styles you need and that's all.

Here is current short How To draft

1. Any opinions on what you have read in How To link? is it clear, is it simple and everything else.
2. Have you been implementing PM system in JS yourself? Share your experience.
3. What tools/libs/frameworks are you using to add PM system to your apps?
4. What was yours PM system's requirements? Only one-to-one communication, only one channel available at the same time, are PM notifications separated from general notifications like on Facebook, etc.
5. Are you using in such cases Service Workers or just sending every N seconds AJAX request to server to get updated data?
6. Any proposals, feedback what would you like to have, what to change related to JS PM system?
7. How are you accessing authenticated user data from JS?
8. How are you getting data from the server (XHR, fetch(), using any framework, library or you own approach, ...)?