The number of subscribers grows every time $rootscope.$on is used

Question

The number of subscribers grows every time $rootscope.$on is used

I currently have an Angular controller that is quite simple:

angular.controller('appCtrl', function ($scope, $rootScope) {
    $rootscope.$on('channel.message', function () {
      // do something here
    }
});

In addition, I have a sidebar on my webpage that directs me to a view associated with the mentioned controller.

The problem arises when each time I click on a link, Angular creates a new instance of the controller. While this is acceptable, I've noticed that the number of subscribers for my 'channel.message' event is continually increasing, which is not ideal.

I am aware that each piece of code simply adds another callback to the queue but I would like to find a way to only have a single subscriber. What are the recommended best practices in this scenario?

Additionally, I'm familiar with using $scope.$on but it's not suitable due to performance implications and the architecture design of the application itself.

javascript angularjs

Answer 1

Answer №1

Consider implementing a named function to call your event handler, which will execute it and then clean it up. Here is an example (also, ensure that $rootscope is properly spelled as $rootScope):

angular.controller('appCtrl', function ($scope, $rootScope) {
    var cleanUp = $rootScope.$on('channel.message', function () {
        // carry out tasks here
    };

    cleanUp();
});

I encountered a similar issue (with multiple callbacks being added to the queue), and the above method resolved it for me.

On a side note, I recommend formatting your controller in this way:

angular.controller('appCtrl', ['$scope','$rootScope', function($scope, $rootScope) {

}]);

Answer 2

Consider implementing a named function to call your event handler, which will execute it and then clean it up. Here is an example (also, ensure that $rootscope is properly spelled as $rootScope):

angular.controller('appCtrl', function ($scope, $rootScope) {
    var cleanUp = $rootScope.$on('channel.message', function () {
        // carry out tasks here
    };

    cleanUp();
});

I encountered a similar issue (with multiple callbacks being added to the queue), and the above method resolved it for me.

On a side note, I recommend formatting your controller in this way:

angular.controller('appCtrl', ['$scope','$rootScope', function($scope, $rootScope) {

}]);

Answer 3

Answer №2

As pointed out by @JoshBeam, the $rootScope.$on() method returns a function that can be used to deregister your listener. Here is an example:

var cleanUp = $rootscope.$on('channel.message', function () {
   // do stuff here
}

The next question is when to trigger this cleanup. Typically, you would want to deregister the listener when the controller is destroyed. Angular provides a convenient way to do this by firing a $destroy event just before tearing down a scope.

$scope.$on('$destroy', function() {
  cleanUp();
};

It's important to note that we are listening for the $destroy event on the $scope (not on $rootScope) in order to capture when the controller is being torn down. Your regular listener can still remain attached to $rootScope.

This pattern is also useful for preventing memory leaks, even if you don't have multiple listeners to worry about.

Answer 4

As pointed out by @JoshBeam, the $rootScope.$on() method returns a function that can be used to deregister your listener. Here is an example:

var cleanUp = $rootscope.$on('channel.message', function () {
   // do stuff here
}

The next question is when to trigger this cleanup. Typically, you would want to deregister the listener when the controller is destroyed. Angular provides a convenient way to do this by firing a $destroy event just before tearing down a scope.

$scope.$on('$destroy', function() {
  cleanUp();
};

It's important to note that we are listening for the $destroy event on the $scope (not on $rootScope) in order to capture when the controller is being torn down. Your regular listener can still remain attached to $rootScope.

This pattern is also useful for preventing memory leaks, even if you don't have multiple listeners to worry about.

Answer 5

Answer №3

In my opinion, it would be beneficial to implement an $onRootScope function, which I have detailed in this response:

How can controllers effectively communicate in AngularJS?

This method simplifies the process by handling event handler deregistration automatically, and its usage is straightforward:

$scope.$onRootScope('barEvent', function(){})

Furthermore, it is worth mentioning that recent updates to angular have mitigated concerns regarding performance impacts of broadcasted events.

Answer 6

In my opinion, it would be beneficial to implement an $onRootScope function, which I have detailed in this response:

How can controllers effectively communicate in AngularJS?

This method simplifies the process by handling event handler deregistration automatically, and its usage is straightforward:

$scope.$onRootScope('barEvent', function(){})

Furthermore, it is worth mentioning that recent updates to angular have mitigated concerns regarding performance impacts of broadcasted events.

The number of subscribers grows every time $rootscope.$on is used

Answer №1

Answer №2

Answer №3

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