Emscripten WebAssembly Module.ready() Promise initialization similar to Module.onRuntimeInitialized

build.sh

#!/bin/bash

docker run --rm -v $(pwd):/src trzeci/emscripten emcc \
  -O0 `# leave uncompressed for example` \
  -s WASM=1 \
  -s EXPORTED_FUNCTIONS="['_hello']" \
  -s EXTRA_EXPORTED_RUNTIME_METHODS="['cwrap']" \
  -o emscripten-module.js \
  --post-js module-post.js \
  hello.c

hello.c

char *hello() {
  return "Hello there. Welcome to WebAssembly.";
}

module-post.js

// Wrap in self-executing function to restrict exposure of Promise vars
(function() {
  Module.ready = new Promise((resolve, reject) => {
    addOnPreMain(() => {
      var api = {
        sayHello: Module.cwrap('hello', 'string', [])
      };
      resolve(api);
    });

    // Propagate error to Module.ready().catch()
    // WARNING: this is a hack based Emscripten's current abort() implementation
    // and could break in the future.
    // Rewrite existing abort(what) function to reject Promise before it executes.
    var origAbort = Module.abort;
    Module.abort = function(what) {
      reject(Error(what));
      origAbort.call(this, what);
    }
  });
})();

test-web-worker.js

self.importScripts('emscripten-module.js');

self.onmessage = event => {
  Module.ready()
  .then(api => {
    if (self.isClosed) return;

    // Interact with Module...
    console.log( api.sayHello() );
  })
  .catch(e => {
    if (self.isClosed) return;

    exitOnError(e);
    console.error('Module failed to initialize', e);
  });
}

// Terminate Worker and prevent Promise microtasks from completing
function exitOnError(e) {
  // "throw e" won't be received by controller. Post as message instead
  self.postMessage({error: e.message});

  self.close();
  self.isClosed = true;
}

test.html

<script src="emscripten-module.js"></script>
<script>
  Module.ready()
  .then(api => console.log( api.sayHello() ))
  .catch(e => console.error('💩', e))
</script>

@surma Great idea changing Module.ready() function to Module.ready property. Much cleaner.