Isn't that mostly just enums?

Is there anything else that doesn't run as valid JS if you strip the types (and maybe some other extra keywords)out?

Genuine question, in my head there's not much, but TS has a few weird corners I maybe haven't used

https://www.typescriptlang.org/tsconfig/#erasableSyntaxOnly covers them all, I strongly recommend running with that option enabled to be future-proof.

enums and decorators mainly. There are also subtleties such as having the ts file extension in imports. Also imports aren't transpiled in cjs so you need to need es modules.

I'm using it in my projects with no issues.