Sure, but if the caller is Javascript then you're running Javascript, not Typescript*, so it makes sense that you're not going to get type safety.

I'm also not sure we're actually disagreeing on anything, so perhaps my reply was pointless. I agree that if you mix JS and TS in the way you describe, you'll have problems. My reply was just to say "yes, and that's not really Typescript's fault", but perhaps you weren't implying that to begin with.

* I'm aware that you can't run Typescript directly, but I hope my point here is clear... you're running a program that wasn't type-checked by TS.

I don't think we're disagreeing either. I didn't mean to suggest that it was Typescript's fault, just that the relationship between TS and JS in theory is something like "TS is a superset of JS" but once you get down to the practice of writing idiomatic reusable code it's more like TS and JS are fully different languages.