Pub/Sub design pattern angularjs service

Question

I've been trying to use the answer here posted by Mark Rajcok

angular JS - communicate between non-dependend services

I am having trouble understanding his answer. Specially this part:

angular.forEach(event1ServiceHandlers, function(handler) {
            handler(some_data);
});

Is the event1ServiceHandlers array populated with functions (here called handler) that is triggered in this forEach loop?

I think it would be much easier to understand with a good example how a publish/subscribe is set up.

I have two services who need to communicate but I want to avoid $rootScope.$broadcast so from what I have read a pub/sub service is the best approach. One of my services need to execute a function on my other service, but that service already has my first service as a dependency so I cannot do the same both ways because of circular dependency.

My question: So assume you have two angularjs services (factory), how does service 1 execute a function on service 2 if service 2 already has service 1 as a dependency. Not using $broadcast and $on

Answer 1

Is the event1ServiceHandlers array populated with functions (here called handler) that is triggered in this forEach loop?

Yes

how does service 1 execute a function on service 2 if service 2 already has service 1 as a dependency

Create service 3, NotificationService as before:

.factory('NotificationService', [function() {
    var event1ServiceHandlers = [];
    return {
        // publish
        event1Happened: function(some_data) {
            angular.forEach(event1ServiceHandlers, function(handler) {
                handler(some_data);
            });
        },
        // subscribe
        onEvent1: function(handler) {
            event1ServiceHandlers.push(handler);
        }
    };
}])

Have service 2 register a callback function with the NotificationService:

.factory('Service2', ['NotificationService',
function(NotificationService) {
    // event1 handler
    var doSomething = function(someData) {
        console.log('S2', someData);
        // do something here
    }
    // subscribe to event1
    NotificationService.onEvent1(doSomething);
    return {
      // define public API for Service2 here
    }
}])

Whenever service 1 wants function doSomething() on service 2 to execute, it can publish the event1Happened event:

.factory('Service1', ['NotificationService',
function(NotificationService) {
    var someData = ...;
    return {
       // define public API for Service1 here
       callService2Method: function() {
         // publish event
         NotificationService.event1Happened(someData);
       }
    }
}])