Javascript feature detect module support for Web Workers

As of Chrome 80, you can create module type workers with new Worker("worker.js", { type: "module" }), and then use module features like import in the worker script. However other browsers are still working on support for this, so using it needs feature detection and a fallback.

Is there a convenient and simple way to feature detect module support for workers?

Note on some platforms (e.g. Cordova) creating workers is actually non-trivial and involves a bunch of workarounds, so something that works in pure JS would be ideal.

As every initOptions features, you can use what I call a "dictionary trap".

It is an Object on which you'd set a property getter (the one you want to test), and let this getter switch a boolean when it's been gotten by the constructor you are testing. This works with a lot of such features, and Worker's type is no exception here.

The only things you'll want to be careful with a Worker is to avoid to actually start one (starting even an empty Worker means a new Event loop has to run, a new JS context and these are not small operations) and avoid it to make an useless network request (even a 404 eats resources).

So here is such a tester, using the string "blob://" has a way to avoid both these situations.

function supportsWorkerType() {
  let supports = false;
  const tester = {
    get type() { supports = true; } // it's been called, it's supported
  };
  try {
    // We use "blob://" as url to avoid an useless network request.
    // This will either throw in Chrome
    // either fire an error event in Firefox
    // which is perfect since
    // we don't need the worker to actually start,
    // checking for the type of the script is done before trying to load it.
    const worker = new Worker('blob://', tester);
  } finally {
    return supports;
  }
}

console.log( supportsWorkerType() );