Author of cljs-ajax here, I'd always favour a straight callback. The async stuff is so easy to add on top it doesn't really seem worth it to add the dependency to the library and complicate matters for people that don't want it.

I guess that's true - core.async adds a lot of stuff you don't want for something as simple as futures/promises.

I wish ClojureScript guys would abstract 'go' macro from core.async in to the clojurescript core, provide well documented protocols that it uses and include implementation for JS Promises by default (then leave core.async to expose chans for those who need channels trough those protocols).

Hell if I knew they wouldn't be against doing this I might even do it my self in a few weeks.

Considering the async nature of JS it makes sense to provide such a construct as a part of language/standard library.

You're right about the underlying JS API being async, and that's why those functions are as well.

I wouldn't mind adding a blocking variant of these functions, and use async internally to make that happen. But, not there yet.