gecko-dev/dom/serviceworkers/test/onmessageerror_worker.js

async function getSwContainer() {
  const clients = await self.clients.matchAll({ type: 'window',
                                                includeUncontrolled: true });

  for (let client of clients) {
    if (client.url.endsWith('test_onmessageerror.html')) {
      return client;
    }
  }
}

self.addEventListener('message', async (e) => {
  const config = e.data;
  const swContainer = await getSwContainer();

  if (config == 'send-bad-message') {
    const serializable = true;
    const deserializable = false;

    swContainer.postMessage(new StructuredCloneTester(serializable, deserializable));

    return;
  }

  if (!config.serializable) {
    swContainer.postMessage({
      result: 'Error',
      reason: 'Service Worker received an unserializable object',
    });

    return;
  }

  if (!config.deserializable) {
    swContainer.postMessage({
      result: 'Error',
      reason: 'Service Worker received (and deserialized) an un-deserializable object',
    });

    return;
  }

  swContainer.postMessage({ received: 'message' });
});

self.addEventListener('messageerror', async () => {
  const swContainer = await getSwContainer();
  swContainer.postMessage({ received: 'messageerror' });
});