Well... modern assembly is monstrously complex. Probably more so than your favorite high level programming language. Modern assembly is generally not a bare minimum, because it's designed to give compilers the interface to run code fast, not to be easy to program by people.
And WebAssembly is a bit of a misnomer since it's not quite your processor's assembly; it's designed to be assembled fast on the client side, while also being memory-safe. Ironically that makes it simpler than actual assembly.
My comment was written with the 8086 emulator in mind. It was great because you could view what was in each register, as well as the inspect any section of memory.
A good assumption is that your WebAssembly binary already has an implementation of malloc which calls grow_memory. It should do something sane, and you shouldn't need to worry: it's similar to having mmap fail on other platforms. What do you do when mmap fail? I usually just give up and abort, but in rare cases I'll do other fancy things.
> Are there high-quality polyfills available for older browsers?
Work had started in 2015 for a solid polyfill, but now all major browser vendors have shipped WebAssembly so that work wasn't seen as necessary anymore.
> How is forward-compatibility expected to be handled? Right now there's only WebAssembly with the core feature-set. What happens as some vendors start to add support for varying features such as GC, SIMD, threads, etc.?
Not that satisfying an answer, but https://github.com/WebAssembly/design/blob/master/FeatureTes...
99% of the time, you proceed to try to write into address (-1) and your process is killed by the supervisor. Despite what many people say, that's a perfectly reasonable thing to do, if you can afford to have your process killed.
The rest of the time, you'll do something very application dependent, like cleaning caches, optimizing for space instead of time, postponing some task, etc.
In a few years WebAssembly might make for a great environment to learn about lower level programming. I've always loved assembly, since it gives you the bare minimum of concepts and tooling from which you can build everything.
What's the reasonable thing to do when a grow-memory instruction returns -1?
How are people using WebAssembly? Are there high-quality polyfills available for older browsers?
How is forward-compatibility expected to be handled? Right now there's only WebAssembly with the core feature-set. What happens as some vendors start to add support for varying features such as GC, SIMD, threads, etc.?