Add function to access instance exports or the instance itself.

[kettle11]

Motivation

I'm trying to write a library that can optionally work-alongside wasm-bindgen or stand-alone without wasm-bindgen based on a feature flag.

My library has some Javascript that requires access to the Wasm instance's exports (to communicate independent of wasm-bindgen), but right now it's quite tricky to expose the instance's exports to my library.

The approach I've found is to stash the value retuned by wasm-bindgen's init on a global variable to access later:

const wasm = await init();
self.kwasm_exports = wasm;

A problem with this approach is that main is called by init so if my library is called by main then it won't yet have access the Wasm exports. A hack is to add a fake entry point to my library and then later call the entry point manually but that's a pretty invasive approach.

Ideally a library user should not have to change any of their Javascript code, they just need to flip a feature flag in my library.

Proposed Solution

If wasm-bindgen exposes a Rust function to access the instance's exports (or the instance itself) instead then that could be used instead to pass the information

This feels similar in purpose to functions like wasm-bindgen's memory function.

Such a function would be a useful escape-hatch for scenarios that are a little bit outside the norm, like my own.