Building an event-based Ajax application

<>p>Dojo has had a publish/subscribe system forever. With 0.9 it gets even better, and this writeup discusses how you can wire up your Ajax application using pub/sub.

If you have an application that uses devices like deferred loading, or â€œparse on demandâ€, wrapping it with an initializer helps keep it that way.

The final code example is:

PLAIN TEXT

JAVASCRIPT:

acme.topic = function(){
// current topic argument hash map
this.current = {};
};
dojo.extend(acme.topic, {
subscribe: function(topic, scope, method, acceptNull){
var hdl = dojo.subscribe(topic, scope, method)
//Initializer - called only once, on subscribe
if(acceptNull || this.current[topic]){
// Converting arg to a non-array if it is not a length> 1
var a = this.current[topic];
var arg = (a == null) ? null : (a.length == 1) ? a[0] : a;
//NOTE! Only accepting string methods
scope[method].call(scope, arg);
}
return hdl;
},
publish: function(topic, args){
dojo.publish(topic, args);
// Store published arg, in the event a subscribe is called later
this.current[topic] = args;
},
unsubscribe: function(handle){
// Pass-through. Could be called directly.
dojo.unsubscribe(handle);
}
})

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