Allow topic subscribers to get an event pre-subscription

[david]

It'd be nice if there was a way for topics to be able to get notified on subscribe if a publisher published before the subscription. Confusing?...

// somewhere this happens:
dojo.event.topic.publish("foo", ...);

// then later...
dojo.event.topic.subscribe("foo", ...);

// it'd be nice to say "let me know about the last one"
dojo.event.topic.subscribe2("foo", ...);
// that would run immediately since we published before the subscription

The overhead may be too expensive to store the last call + arguments for all published events. If that's the case, I propose that we have a special kind of subscription, "let me know, but who cares what's on the wire", so you can at least get notified buy you don't care about any args.

dojo.event.topic.subscribeAlert("foo", function() {
  alert('foo ran at some point, maybe even before I subscribed!');
});

[dylan]

this would be really nice to have... basically getting a history of messages sent to the topic

[tk]

I agree... (if its to be had... now would be the time to have it (pre 0.9stable or atleast pre 1.0)

-Karl

[alex]

there are several possible use cases, the degenerate one being covered by dojo.Deferred in 0.9. We need a better use case to specialize topics for this.

[Adam Peller]

sounds like Deferreds are good enough? Close?

[dylan]

closing as Deferreds solve the most common use case.