Modernize emscripten usage ("env" "pthread_self": function import requires a callable)

[PeterZhizhin]

If I recompile with a new emscripten compiler version (3.1.64), I get the following error on importing the WebAssembly module:

LinkError: WebAssembly.instantiate(): Import #0 "env" "pthread_self": function import requires a callable
    at 0026ddb4-d116-4418-b697-5ee71eb6c206:157:36
(anonymous) @ 0026ddb4-d116-4418-b697-5ee71eb6c206:157
Promise.then
self.onmessage @ 0026ddb4-d116-4418-b697-5ee71eb6c206:159

The reason for this is that a more recent emscripten (less than ~3 years old) compiler exports additional symbols that we are not defining when calling instantiate.

When compiling as a regular module, emscripten will generate additional JS output file that actually loads all functions:

em++ -std=c++11 sorter.cpp -o sorter.js -s WASM=1 -s USE_PTHREADS=1 -msimd128

This generates the following files:

sorter.js
sorter.wasm

The sorter.js file will actually load the sorter.wasm file into a Module variable. This variable can then be used to access defined C++ functions.

This approach will be more future-proof, since the generated .js file will be different depending on the compiler version.

I'd like to know if something like this was considered. And if it wasn't used, then why.