firefox/dom/messagechannel/tests/sharedWorker_messageChannel.js

/* eslint-env worker */

onconnect = function (evt) {
  var mc = new MessageChannel();

  evt.ports[0].postMessage(42, [mc.port2]);
  mc.port1.onmessage = function (e) {
    mc.port1.postMessage(e.data);
  };
};