Attach a callback to a publish

Question

I was wondering whether anyone knew of a way to attach an event/callback to a dojo publish when the event that is published completes.

I am publishing something as a delegated task, and when the delegated task completes I want to make some UI changes.

Let me know if you know how or if you know that it's not possible.

---

EDIT: I guess I could also do what I wanted if I was able to return a value to the publisher after the event published finishes.

Answer 1

I don't know of a "correct" way to do this but you could try using a separate channel and enforcing the connection "by convention":

dojo.subscribe('fooChannel', function(){
     ....
     dojo.publish('fooChannelComplete', [...]);
});

A helper function to make this more seamless:

function add_to_foo(f){
    dojo.subscribe('fooChannel', function(){
        var ret = f.apply(this, arguments);
        dojo.publish('fooChannelComplete', [ret]);
    });
}

Answer 2

Let's try something like this

// publisher side
var d = new dojo.Deferred();
dojo.publish("my/channel",[d]);
// ... do some extra asynchronous work , server request ...
result = goterror ? "error" : "ok";
if (!error) d.callback(result); else d.errback(result);

// listener side
dojo.subscribe("my/channel",function(d) {
  // let's wait for the server to respond ( or maybe its already done )
  d.then(function(result) {
    // result is "ok"
  },function(params) {
    // result is "error"
  });
});

Answer 3

Building on @Sebastien's premise:

//publisher
var deferred = new Dojo.deferred();
var successFunction = function(){
  console.log('task succesfully completed');
};

var errorFunction = function(){
  console.log('task did not succesfully complete');
};
//when our deferred object is done, invoke either successFunction or errorFunction
dojo.when(deferred, successFunction, errorFunction);

dojo.publish("someTopic",[deferred]);




//topic subscriber code
dojo.subscribe("someTopic",function(deferred) {
  //do whatever delegated task is needed.
  //...

  //task completed successfully, invoke the `successFunction` defined on the publisher
  deferred.callback();  

  //or if task did not complete successfully invoke `errorFunction` defined on the publisher
  //deferred.errback();

});

Same premise, but using dojo.when which IMO is nicer syntactic sugar.