In fact there’s almost certainly more ways, too. You could probably transpile WASM to JVM bytecode. These things are most useful when you already are in the JVM anyways, I can’t imagine most people writing software in pure Rust would jump for this, especially given that WASM has a lot to offer for this use case already and has good momentum. I see it as a better fit, with useful security guarantees and a simple design.
The benefits of the JVM still stand out to me personally. Run anywhere, generate machine code at run time most place, world class optimizing compiler, battle tested & ready to deploy, integration with existing code base for gradual rewrites, etc.
Wasm is a good idea but it's going to need to reimplement a lot of existing code (optimizing + jit).
Doable and maybe it will convince people to do what has been a great idea first widely deployed by Java: compiled language in an abstract machine.
The JVM had many chances to realize that goal. Java applets, J2ME, etc. I’m not sure which particular issue really kept it from keeping mindshare. I don’t think the virtual machine itself was ever really the problem.
Still, since the Java platform didn’t capture this use case of a general purpose abstract machine, it makes a whole lot of sense to develop something like WASM. It’s a much more neutral platform to build on.
In particular we actually don’t need to go through all of the things Java went through; we have a wealth of knowledge about what things work and what things don’t work so well. Yes, its a new JIT, but not that new: from my understanding typically the JavaScript JIT machinery is reused for the WASM JIT in browsers.
If JavaScript JITs are anything like Java JITs then it might be that most of the performance-improving optimizations are based on optimizations of how Java/JavaScript operate and recognizing specific patterns that can be replaced with simpler instructions to improve performance. The JavaScript JITs help with the machine code generation but not necessarily with other higher-level optimizations.
