gecko-dev/dom/workers/test/webSocket_sharedWorker.js

onconnect = function(evt) {
  var ws = new WebSocket("ws://mochi.test:8888/tests/dom/base/test/file_websocket_hello");

  ws.onopen = function(e) {
    evt.ports[0].postMessage({type: 'status', status: true, msg: 'OnOpen called' });
    ws.send("data");
  }

  ws.onclose = function(e) {}

  ws.onerror = function(e) {
    evt.ports[0].postMessage({type: 'status', status: false, msg: 'onerror called!'});
  }

  ws.onmessage = function(e) {
    evt.ports[0].postMessage({type: 'status', status: e.data == 'Hello world!', msg: 'Wrong data'});
    ws.close();
    evt.ports[0].postMessage({type: 'finish' });
  }
}