I see this being said, but from what I've seen async handling is generally not very graceful; with that said, Promises are a very simple but powerful API that seem to handle the problem fairly elegantly.
That is why I'm surprised. I just don't know what the alternative is supposed to be! Can you point me to a language and a library that you would say does a better job of handling asynchronicity than Promises?
EDIT: To elaborate a bit, what I don't like about (JS) Promises, in hindsight, is that 1) they seem to infect my entire codebase, and 2) making non-async code async is usually nontrivial. In Elixir it's basically a matter of 'telling' a function or an entire module to go do it's thing in another process and report back when done. It means in many cases I only need to change the caller side of things and the code that runs async itself looks the same as the sync code. And that's not even the best part of (Erlang style) processes!