gistfile1.js

var Observer = dojo.extend(function(){}, {
  observe: function(promise){
    this.onStart(promise);
    promise.then(dojo.hitch(this, "onEnd"));
    return promise;
  },
  
  onStart: function(promise){},
  onEnd: function(result){}
});

var observer = new Observer;
dojo.connect(observer, "onStart", function(promise){
  console.log("Started with promise", promise);
});
dojo.connect(observer, "onEnd", function(result){
  console.log("Got result", result);
});

var dfd = new dojo.Deferred;
observer.observe(dfd.promise);
dfd.resolve("Done");