Oh yeah, I'll mention JSDoc @type tags - hard pass, if you can. Comments should have NO EFFECT AT ALL WHATSOEVER on code. They're comments. Everything should be identical with and without them, they are 100% disposable. Moving any type of functionality into comments makes them brittle and now they can't be stripped out.

The suggestion to add a `.d.ts` file is good - it allows people who do use TS to be able to use strong/static typing while using your library, without you needing to add any kind of type support within your library. Just make sure it stays updated ;)