gistfile1.js

var worker = {};
worker.start = function(uri, data) {
  var deferred = new Deferred();
  var worker = new Worker(uri);

  worker.onmessage = function(event) { deferred.call(event); };
  worker.onerror = function(event) { deferred.fail(event); };
  worker.postMessage(data);
  deferred.canceller = function() { worker.terminate() };

  return deferred;
}

worker.start("hello_worker.js", "world").next(function(event) {
  alert(event.data);
});

// hello_worker.js
//
// onmessage = function(event) {
//   postMessage("hello " + event.data);
// };