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

build.sh

#!/bin/bash

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

// Module.ready resolves when WASM instantiates. (ready is now a property and not function via @surma fork)
Module.ready = new Promise(function(resolve, reject) {
  addOnPreMain(function() {
    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 = this.abort;
  this.abort = function(what) {
    reject(Error(what));
    origAbort.call(this, what);
  }
});

test-with-worker.html

<script>
  const worker = new Worker('web-worker.js');

  worker.onmessage = event => {
    const error = event.data.error;
    if (error) {
      console.error('WASM failed to instantiate', error);
    }
  }

  // post a few messages and view console
  for (let i=0; i<10; i++) {
    worker.postMessage(i);
  }
</script>

test-without-worker.html

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

web-worker.js

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

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

    const data = event.data;

    // Interact with Module...
    console.log( data, 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;
}

have you phread version?