Strategy for creating async extensions

[libitx]

Hi. I'm trying to create some extensions that call javascript code that needs to run asynchronously. In effect this returns a Promise to Lua, instead of the resolved value.

I see an open (#2) issue from 2017 that seems related but hasn't been resolved. This problem is proving a bit of a blocker to my project at the moment, so I'd be happy to contribute a PR to move this forward, but I'm not sure exactly what the strategy should be. Did you have any ideas how to resolve #2?

Or is current best strategy just to avoid async code in extensions?

[daurnimator]

Please keep discussion in #2 rather than opening a new issue.