> I'm curious if the runtime flag to enable JITless mode could also be enabled at compile time, removing the JIT compiler from the binary entirely. That could be really useful for projects where memory comes at a premium (and performance is not a major concern), like micropython but for JavaScript.

Theoretically yes, but this is not implemented. It should not be too hard to drastically reduce binary size with a build-time flag.

> I assume this also doesn't support WASM when the JIT is disabled (or rather, when you can't write to executable memory), but if it did it could be a neat way to write decently performant software for tiny systems with just some JavaScript "glue".

Correct, wasm is currently unsupported. Interpreted wasm is possible in the future, but would likely be very slow.