WASM loader does not expose importObject

WebAssembly modules are able to import foreign Javascript functions and memory objects that are passed in the second parameter of WebAssembly.instantiate(...). Unfortunately the current WASM loader is hard-coded to call instantiate with no import object.

https://github.com/parcel-bundler/parcel/blob/master/src/builtins/loaders/wasm-loader.js https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/instantiate

The simplest solution would be to have the WASM loader instead run WebAssembly.compile(...) and return the compiled WebAssembly.Module, so the user can call WebAssembly.instantiate(...) with whatever parameters they need. I think that’s how Webpacks wasm loader works.

[linclark]

Yep. I kinda like the way webpack is planning to approach this (I think): imports in WASM files get mapped to module imports the same way imports in JS do.

You’re correct, this is the right approach. WASM modules will eventually be ES modules, so imports/exports should work the same as they do in JS. I will likely be championing this over the next few months. Work will be tracked in https://github.com/WebAssembly/design/issues/1087

The problem is that the current Rust wasm backend always generates only a single import, and it’s always called “env”

The webpack folks also brought this up. If no one responds with a plan to address this, I’ll bring it up in our biweekly WASM toolchain meeting (which is next Tuesday) and see if I can figure out what the plan is.

[zakcutner]

It would be really nice to have support for importObject – a killer feature of WASM is the ability to call JS functions from WASM modules (as well as the other way round of course)!

I feel that you shouldn’t have to compile WASM modules already knowing the paths of JS files they use. It would be nice to simply have them as standalone binary modules to which you can pass in imports they need to run (in keeping with the JS WebAssembly.instantiateStreaming() API).

Besides, this would also open up support for wasm_bindgen as well as other existing WASM compilers. @hitecherik and I thought perhaps a syntax like this would be preferable (and compatible with the current import syntax)…

const module = await import("module.wasm")(importObject);
module.foo();