I looked into JS as an alternative, given that ES6 cleaned up a lot of the things that had previously been bugging me about JS. I thought JS must be well-suited for embedding usecases, and the vastly larger language community, compared to Lua, must be an advantage of some sort.

But I ended up concluding that I still don't want to go anywhere near JS.

It's like browser-based use of JS and node-based use of JS are sucking the air away from JS's potential as a language for embedding.

e.g. Nashorn was part of the Java standard API in Java 8 but then got dropped. There's project Detroit to try to replace it, but it doesn't seem to be going anywhere. Most people interested in embedding JS in Java will presumably want node compatibility, even though node is not a great architecture for embedding, so that's what GraalJS is doing, but it comes at the cost of a loss of portability to non-Graal Java environments. A widely-used way of embedding JS in C# is by actually invoking the system browser through WebView in some weird and convoluted way. ...it's things like that which make me recoil in horror. Meanwhile Lua for Java and Lua for C# is just quietly and humbly in existence and using a sane architecture.

...and then JS libraries are full of this async-stuff with promises and whatnot, and I'm reluctant to go anywhere near that if I'm positively certain that it serves absolutely no purpose in the applications I actually intend to build and comes at the price of making code so much more complicated and unreadable.