Consider refactoring the APIs to use Future s.

[MaulingMonkey]

Web MIDI support is made awkward in a couple of places by the browser's use of async/deferred callbacks:

• Getting input/output device lists (need to request access first)
• Opening/closing devices

Futures should, at least in theory, keep the API relatively sane (allowing you to write async code or to simply .wait() in traditional sync code)

The wasm_bindgen_futures crate provides JsFuture, which looks like it should make this quite straightforward.

[Boscop]

If that is done, async not be the default/only way, the blocking way should still be possible.