rootScope broadcast vs scope emit

Question

Now that the performance difference between  broadcast and  emit has been eliminated  is there any reason to prefer  scope  emit to  rootScope  broadcast   They are different  yes     emit is restricted to the scope hierarchy  upwards  - this may be good  if it fits your design  but it seems to me a rather arbitrary restriction    rootScope  broadcast works across all that choose to listen to the event  which is a more sensible restriction in my mind   Am I missing something   EDIT   To clarify in response to an answer  the direction of the dispatch is not the issue I m after   scope  emit dispatches the event upwards  and  scope  broadcast - downwards  But why not always use  rootScope  broadcast to reach all the intended listeners

User · Answer

Use RxJS in a Service

What about in a situation where you have a Service that's holding state for example. How could I push changes to that Service, and other random components on the page be aware of such a change? Been struggling with tackling this problem lately

Build a service with RxJS Extensions for Angular.

<script src="//unpkg.com/angular/angular.js"></script>
<script src="//unpkg.com/rx/dist/rx.all.js"></script>
<script src="//unpkg.com/rx-angular/dist/rx.angular.js"></script>

var app = angular.module('myApp', ['rx']);

app.factory("DataService", function(rx) {
  var subject = new rx.Subject(); 
  var data = "Initial";

  return {
      set: function set(d){
        data = d;
        subject.onNext(d);
      },
      get: function get() {
        return data;
      },
      subscribe: function (o) {
         return subject.subscribe(o);
      }
  };
});

Then simply subscribe to the changes.

app.controller('displayCtrl', function(DataService) {
  var $ctrl = this;

  $ctrl.data = DataService.get();
  var subscription = DataService.subscribe(function onNext(d) {
      $ctrl.data = d;
  });

  this.$onDestroy = function() {
      subscription.dispose();
  };
});

Clients can subscribe to changes with DataService.subscribe and producers can push changes with DataService.set.

The DEMO on PLNKR.

User · Answer

tl dr  this tl dr is from  sp00m s answer below       emit dispatches an event upwards      broadcast dispatches an event downwards   Detailed explanation   rootScope  emit only lets other  rootScope listeners catch it  This is good when you don t want every  scope to get it  Mostly a high level communication  Think of it as adults talking to each other in a room so the kids can t hear them    rootScope  broadcast is a method that lets pretty much everything hear it  This would be the equivalent of parents yelling that dinner is ready so everyone in the house hears it    scope  emit is when you want that  scope and all its parents and  rootScope to hear the event  This is a child whining to their parents at home  but not at a grocery store where other kids can hear     scope  broadcast is for the  scope itself and its children  This is a child whispering to its stuffed animals so their parents can t hear

User · Answer

Eddie has given a perfect answer of the question asked  But I would like to draw attention to using an more efficient approach of Pub Sub  As this answer suggests   The  broadcast  on approach is not terribly efficient as it broadcasts to all the scopes Either in one direction or both direction of Scope hierarchy   While the Pub Sub approach is much more direct  Only subscribers get the events  so it isn t going to every scope in the system to make it work   you can use angular-PubSub angular module  once you add PubSub module to your app dependency  you can use PubSub service to subscribe and unsubscribe events topics  Easy to subscribe     Subscribe to event var sub   PubSub subscribe  event-name   function topic  data             Easy to publish PubSub publish  event-name         prop1  value1      prop2  value2      To unsubscribe  use PubSub unsubscribe sub   OR PubSub unsubscribe  event-name     NOTE Don t forget to unsubscribe to avoid memory leaks

User · Answer

scope  emit   This method dispatches the event in the upwards direction  from child to  parent     scope  broadcast  Method dispatches the event in the downwards direction  from parent to child   to all the child controllers     scope  on  Method registers to listen to some event  All the controllers which are listening to that event get notification of the broadcast or emit based on  the where those fit in the child-parent hierarchy    The  emit event can be cancelled by any one of the  scope who is listening to the event   The  on provides the  stopPropagation  method  By calling this method the event can be stopped from propagating further   Plunker  https   embed plnkr co 0Pdrrtj3GEnMp2UpILp4   In case of sibling scopes  the scopes which are not in the direct parent-child hierarchy  then  emit and  broadcast will not communicate to the sibling scopes     For more details please refer to  http   yogeshtutorials blogspot in 2015 12 event-based-communication-between-angularjs-controllers html

User · Answer

They are not doing the same job   emit dispatches an event upwards through the scope hierarchy  while  broadcast dispatches an event downwards to all child scopes

User · Answer

I made the following graphic out of the following link  https   toddmotto com all-about-angulars-emit-broadcast-on-publish-subscribing     As you can see   rootScope  broadcast hits a lot more listeners than  scope  emit   Also   scope  emit s bubbling effect can be cancelled  whereas  rootScope  broadcast cannot

[angularjs] $rootScope.$broadcast vs. $scope.$emit

Use RxJS in a Service

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