[BUG] wasm is not ready when DOMContentLoaded fires and does not trigger an event when it is loaded

[JasonGross]

Describe the bug
In
fiat-html.tar.gz (unpack the tar.gz, run python -m http.server 8000 in the fiat-html directory, and then navigate to http://localhost:8000/?argv=%5B%22-h%22%5D&interactive&wasm in Chrome), the code fails with "ReferenceError: synthesize is not defined". But if you change the setTimeout in main.js to be 1000 instead of 1, so that it waits a full second, then the code works fine.

The .tar.gz contains the standalone wasm_fiat_crypto.ml used to generate the wasm with -package unix -w -20 -g -package js_of_ocaml -linkpkg and then wasm_of_ocaml --source-map --no-inline.

Expected behavior
All exported functions should be available by the time DOMContentLoaded fires

Versions
Chrome Version 119.0.6045.160 (Official Build) (64-bit)
ocaml-option-fp.1,ocaml-variants.4.14.1+options

$ wasm_of_ocaml --version
5.3.0+git-f517bbca-dirty
$ ocamlc --version
4.14.1

[vouillon]

I don't think there is any way to fix that since compiling and instantiating WebAssembly code is asynchronous.

Your Wasm code should somehow signal when it is ready.

[JasonGross]

Could the generated .js file be made to trigger some event when the wasm code is ready? It seems like the cleanest place to do this is using the Promise of the async function in the generated .js wrapper, you could insert something like

.then((value) => {
  dispatchEvent(new CustomEvent('wasmCodeLoaded', {detail: {src}} ));
}).catch((error) => {
  dispatchEvent(new CustomEvent('wasmCodeLoadingError', {detail: {src, error}}));
})

And perhaps wasm_of_ocaml could take command line arguments for naming these events?

It seems cleaner to me to do it in the autogenerated javascript code wrapper, and matches more closely with js_of_ocaml behavior, rather than requiring the source program to add some extra code to deal with this.