How to use TypeScript lib in JavaScript app

[OP-Klaus]

Hi all. I'm wondering what is the recommended way to achieve what I'm wanting:
For context, my team and I develop some large applications that currently span multiple repositories, including one "core" repository, which is used by many of them, called core. Some of the applications are in TypeScript, but most of the bigger ones are in JavaScript.
We are in the process of trying to bring everything into Nx, and we have converted core to TypeScript already, and added it as a lib in the new Nx repository. We don't have time to convert every app to TypeScript immediately.

So the question is:
What is the best way to have a TypeScript lib that can be used by both TypeScript and JavaScript apps? ie. how do we reference our buildable TS lib from inside a JS application in the same Nx workspace?