I think we're talking about two different problems. You don't need to switch your whole project to typescript to use typescript, I'm just talking about the head

I think we're talking about two different problems. You don't need to switch your whole project to typescript to use typescript, I'm just talking about the headache that comes from mixing something like vanilla js, webpack, closure compiler, and typescript. Vanilla js with JSDoc tends to play well with everything, so I think it's well suited for a library.