[jfbastien]

> What's the reasonable thing to do when a grow-memory instruction returns -1?

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...