[zmw]

You can access web APIs and access DOM in wasm today (from your comment you seem to be unware of that?). I just wrote a tiny web app in Rust with wasm-bindgen, and it’s pretty good already. With wasm-bindgen interfacing is pretty manual at the moment — you need to declare the APIs you need in Rust by hand, but an app without dependencies that modify the DOM generates a wasm file that’s only a few KB. My app pulls in quite a few libs and ended up with a ~700KB wasm build — a bit larger than satisfactory, but definitely in the tolerable range.

[deathanatos]

I know wasm-bindgen exists, and I presume it works. But it's black magic.

Near as I can tell, it serializes everything through the linear memory; this would have a huge impact on the performance of both ends, would it not? (Particularly if you wanted to do DOM manip w/ it.) I believe this is what the article means here,

> You need to pass values into the WebAssembly function or return a value from it. This can also be slow, and it can be difficult too.

> There are a couple of reasons it’s hard. One is because, at the moment, WebAssembly only understands numbers. This means that you can’t pass more complex values, like objects, in as parameters. You need to convert that object into numbers and put it in the linear memory. Then you pass WebAssembly the location in the linear memory.

[zmw]

I only spent about an hour on the rust + wasm app for fun, so I treated wasm-bindgen and wasm-pack as black boxes and didn't really try to understand the inner workings. You're probably right about serialization, but I'm not sure it has to copy huge buffers around.

Look, the supported types in wasm-bindgen are somewhat restricted. The full list is here [1]. Other than "atomic" types like numbers and pointers (I assume the opaque types are treated as pointers too), the interesting one are str/String (basically &[u8] under the hood) and number slices. It's apparently not great if you have to copy these around, but since these are well-aligned, why can't you just pass the starting address and length? Again, I don't know enough about wasm or its current state to say if this is doable. Maybe it doesn't like "someone else's memory" at the moment.

(By the way, wasm-bindgen allows you to access pub fields of structs from JS, but they have to be Copy. That is to say, the opaque types are not completely opaque, but I'm not sure if the pub field access is achieved through implicit getter methods or serialized in the first place.)

Anyway, the frictions might be a big problem if you're doing React-style DOM re-renders all the time, but in my app, I'm only running the computation heavy and memory sensitive tasks in wasm, and communications are few and far between, making it a non-issue.

[1] https://rustwasm.github.io/wasm-bindgen/reference/types.html