However...

I'm also wanting to write it such that a modern UI library / framework (e.g. React) can extend this library as a wrapper, and in essence, 'recreate' the same component library API out of React components instead of raw JS ones. So there's this vanilla JS library doing most of the work, but a React wrapper on top as well to help those on a React stack.

I've read the React docs[1] on how to integrate React with a plugin that you can't control - which were very helpful- however, I'm looking for best practices on how to build a plugin (obviously that I can control) that plays as nicely as possible with React.

I realize this is pretty high-level stuff, but any resources, tips from experience, or examples of JS libraries like this (that is, created with framework integration in mind from the start) that you've seen or worked on / with would really help!

[1] https://reactjs.org/docs/integrating-with-other-libraries.html#integrating-with-dom-manipulation-plugins