Even in Rust, it only looks like that in this very specific use case and is usually completely hidden from the programmer. It's the desugared output of a library.

Usually it would look like this in Rust:

fn get_user(&self) -> impl Future<Output = User>;

This isn't exactly the same functionally, but for most use cases it works just fine. The difference is that this uses static dispatch instead of dynamic dispatch and therefore can't support dynamically returning two different structs that both implement Future, it has to be one type.

Not in dynamic languages, ie JavaScript

It is. It's not visible if you the types aren't written, but under the hood, that's the type of things like this.

Ehm. No. JavaScript will return a Promise. It’s “type” is Object as pretty much anything else in JavaScript.

But isn't a Promise for all intents and purposes the same as a Future here?

Yes, but I think they are emphasising that only a promise will be returned. Any further type information is not given

Check out structural typing. I would say it’s the type system JavaScript uses for non-primitive values. The “dynamic” appearance is just that JavaScript doesn’t center the type system in its UX.