Very simple - in Java, almost any IO operation in blocking. Exceptions are the stuff in the NIO package, thread interruption and signalling, and maybe process termination.

In TypeScript at least, async-ness is encoded in the type system, because async/await is just syntactic sugar for Promise/then/catch.

Well, JS is paired with a single-threaded execution model, so you only have concurrency to worry about. C#, Java has proper multithreading as well, that gives another dimension to the problem.

Kotlin has multithreading, and it also puts `suspend` in the type system.

Some more examples: Rust, Python (with most/all? type checkers), C# all bake this into their type systems.

This is more due to the fact that Kotlin doesn’t control its backend and is designed to work with a language that already includes this model, js.

What if file exists operation MUST be sync?

Then you don’t start it in a virtual thread. Your calls automatically become blocking or not blocking depending on your callsites, which is the proper place to decide that.

So it still has colors?