That would only be required for data on the GC heap. Yes, you would have to implement an FFI for communicating with the browser, especially for any callbacks i

That would only be required for data on the GC heap. Yes, you would have to implement an FFI for communicating with the browser, especially for any callbacks into the browser that take allocated memory, but it is far better to build a hygienic FFI if you want to use a GC language than re-architect the browser with GC support. It can be done. There may be pain, but the pain can be managed. EDIT: by that I mean that one would need to maintain two heaps. One for data that interacts with the browser and that is wrapped by the FFI as external resources, and one for the internal system itself, which can be managed via GC. Only the WebAssembly code would have to manage GC roots, which can be done as per any GC language.