desired usage

A true shim for the WebAssembly global would be best, but is probably impossible, due to the async nature of communcation with WebView

A nice second best would be an almost-shim, a la:

// load
const wasmModule = await WebAssembly.instantiateStreaming('/path/to/assets/somemodule.wasm')
// use as with WebAssembly, but everything's async
const result = await wasmModule.instance.exports.doSomething('hi', { blah: 'ho' })

potential approaches:

• via webview component (will only support async functions)
• for sync invocations
  • maybe it's possible to bundle a VM, e.g. https://github.com/perlin-network/life
  • hacks, such as:
    • iOS: workaround/hack via javascript prompt() function: https://stackoverflow.com/questions/29249132/wkwebview-complex-communication-between-javascript-native-code/49474323#49474323
    • Android: - sync JS via native-side loop + timer: https://stackoverflow.com/questions/37475073/android-main-thread-blocking-webview-thread

for now, it looks like async is enough

JS only vs JS + Native-side WebView manipulation

JS-only would be cleanest, but we may need additional control over the WebView, e.g. to make it load .wasm from local assets. Still need to experiment to see if fetch('/path/to/somemodule.wasm') can be made to work

alternatives to WASM

• emscripten
• convert wasm to JS with binaryen's experimental wasm2js. But at this point you might as well just use emscripten to convert to asm.js in the first place

iOS nonsense

• WebAssembly broken on iOS 11.2: https://github.com/aspnet/Blazor/issues/73#issuecomment-364213098
• no support for WebAssembly.instantiateStreaming/compileStreaming()
• loading local files from WebView: https://stackoverflow.com/questions/24882834/wkwebview-not-loading-local-files-under-ios-8/28676439#28676439

How to load WASM

• docs: https://developers.google.com/web/updates/2018/04/loading-wasm
• extending RN packager (if embedding in .wasm in bundle): facebook/react-native#505 (comment)

Questions

• how to load WASM in WebView?
  • fetch() from local assets (so far unsuccessful)
  • load WASM from some server - requires being online, but can maybe be cached until next app upgrade
  • inline in HTML
  • inline in main bundle, send as base64 via postMessage. This sounds slow. Monero's wasm alone is a >1MB binary.
  • load from native-side (don't know if possible)

potentially useful tools / modules / SO questions

comlink module that creates a proxy object that works across postMessage. Will need proxy-polyfill

wkwebview (not exactly what's needed but could be helpful)

• loading files from doc folder: https://stackoverflow.com/questions/39336235/wkwebview-does-load-resources-from-local-document-folder?rq=1
• requesting files from doc folder: https://stackoverflow.com/a/49637828 (same as https://stackoverflow.com/a/49638654)
• allowing wkwebview to access a local file (sort of): https://stackoverflow.com/a/52953127
• https://stackoverflow.com/questions/51538919/wkwebview-load-files-from-both-bundle-and-document-directory
• Looks useful: load resources from relative path using local html in uiwebview https://stackoverflow.com/a/8436281