I'm pretty sure you'll will still need a JS shim to talk to most web APIs. For instance the Mozilla DOM experiments seems to use a special JS variant with a 'use component' header (similar to the old 'use asm' for asm.js) as shim, but the JS shim is still there. The component model can marshal 'record types' between different WASM modules, but AFAIK not between a WASM module and a web API.