What's the correct way to communicate between controllers in AngularJS? Ask Question

Edit: The issue addressed in this answer have been resolved in angular.js version 1.2.7. $broadcast now avoids bubbling over unregistered scopes and runs just as fast as $emit.

So, now you can:

• use $broadcast from the $rootScope
• listen using $on from the local $scope that needs to know about the event

Original Answer Below

I highly advise not to use $rootScope.$broadcast + $scope.$on but rather $rootScope.$emit+ $rootScope.$on. The former can cause serious performance problems as raised by @numan. That is because the event will bubble down through all scopes.

However, the latter (using $rootScope.$emit + $rootScope.$on) does not suffer from this and can therefore be used as a fast communication channel!

From the angular documentation of $emit:

Dispatches an event name upwards through the scope hierarchy notifying the registered

Since there is no scope above $rootScope, there is no bubbling happening. It is totally safe to use $rootScope.$emit()/ $rootScope.$on() as an EventBus.

However, there is one gotcha when using it from within Controllers. If you directly bind to $rootScope.$on() from within a controller, you'll have to clean up the binding yourself when your local $scope gets destroyed. This is because controllers (in contrast to services) can get instantiated multiple times over the lifetime of an application which would result into bindings summing up eventually creating memory leaks all over the place :)

To unregister, just listen on your $scope's $destroy event and then call the function that was returned by $rootScope.$on.

angular
    .module('MyApp')
    .controller('MyController', ['$scope', '$rootScope', function MyController($scope, $rootScope) {

            var unbind = $rootScope.$on('someComponent.someCrazyEvent', function(){
                console.log('foo');
            });

            $scope.$on('$destroy', unbind);
        }
    ]);

angular
    .module('MyApp')
    .config(['$provide', function($provide){
        $provide.decorator('$rootScope', ['$delegate', function($delegate){

            Object.defineProperty($delegate.constructor.prototype, '$onRootScope', {
                value: function(name, listener){
                    var unsubscribe = $delegate.$on(name, listener);
                    this.$on('$destroy', unsubscribe);

                    return unsubscribe;
                },
                enumerable: false
            });


            return $delegate;
        }]);
    }]);

angular
    .module('MyApp')
    .controller('MyController', ['$scope', function MyController($scope) {

            $scope.$onRootScope('someComponent.someCrazyEvent', function(){
                console.log('foo');
            });
        }
    ]);