observable.js

var observableStream = Rx.Observable.create(function (observer) {
  var url1 = 'http://hello-universe.com';
  var url2 = 'http://hello-world.com';
  var defaultValue = {};
  
  observer.onNext(defaultValue);
    
  $.get(url1).then(function(data) {
    observer.onNext(data);
    return $.get(url2);
  }).then(function(data) {
    observer.onNext(data);
    observer.onCompleted();
  });
});