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 answ

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);
       }
    }
}])

Answer 2

In his example, NotificationService is a new service that any of the existing services would depend on. He provided an implementation of Service1 but Service2 would essentially be the same...both depend on NotificationService and neither know about each other.

Service1 and Service2 each subscribe to events by calling NotificationService.onEvent1(event1Happened); and trigger events by calling NotificationService.event1Happened(my_data);.