How to check the dojo topic event is subscribed or unsubscribed - dojo

Question

someMethod : function() {
if ( !this._evt ) {
this._evt = topic.subscribe("some-evt", lang.hitch(this, "_someOtherMethod"));
} else {
this._evt.remove();
//Here this just remove the listener but the object this._evt is not null
}
},
Here i just want to know how can we came to know that this class already subscribed to the 'some-evt'.
I don't want to set this._evt = null; to null after this._evt.remove();

Answer 1

Sorry, but the dojo/topic implementations typically do not provide a list of topics that have been published/subscribed to, and neither who published/subscribed to that topic. Dojo’s implementation conforms to this standard that there is no built-in mechanism to acquire a list of topics. Note that dojo/topic only have 2 functions, publish and subscribe.
You should implement your own idea, something like a mixin with a function to subscribe to a topic and keep a track of topic names registered, this is just an idea
The _TopicMixin.js
define(["dojo/topic"], function(topic){
return {
topicsIndex: {},
mySubscribe: function(topicName, listener){
this.topicsIndex[topicName] = topic.subscribe(topicName, listener);
}
myUnsubscribe: function(topicName){
if(this.topicsIndex[topicName]){
this.topicsIndex[topicName].remove();
delete this.topicsIndex[topicName];
}
}
amISubscribed: function(topicName){
return this.topicsIndex[topicName];
}
};
});
How you can use it
define(["dojo/_base/declare","myApp/_TopicMixin"], function(declare, _TopicMixin){
return declare([_TopicMixin], {
someMethod : function(){
if ( !this.amISubscribed("some-evt") ) {
this.mySubscribe("some-evt", lang.hitch(this, "_someOtherMethod"));
} else {
this.myUnsubscribe();
}
}
});
});
Hope it helps