My understanding is that WASI uses a calling convention that makes sense for direct use with languages like C. At the same time, there's ongoing work on WebIDL to make it into a practical, language-neutral API binding layer, with WebIDL bindings.

I'm curious why WebIDL doesn't meet the needs for WASI. When APIs for new capabilities are exposed, what is the advice for API designers, in terms of choosing between WebIDL and WASI-style APIs? What would be the relationship with WebIDL if WASI comes to the Web? If WASI is a path towards exposing new capabilities, like mmap, to the Web, how should those be accessible from JavaScript?