Angular: Exploring the differences between $rootScope variable and event handling

Question

Angular: Exploring the differences between $rootScope variable and event handling

I have a dilemma with an app that handles user logins. As is common in many apps, I need to alter the header once the user logs in. The main file (index.html) utilizes ng-include to incorporate the header.html

I've come across two potential solutions (as I am relatively new to Angular, both may be flawed):

1) utilize $rootScope.broadcast()

Upon user login, I broadcast a message from the auth.js (which resides within a factory) that the controller in the header intercepts.

The auth.js

$rootScope.$broadcast('logged',user);

The controller.js

$scope.$on('logged', function(evnt, message){
      $scope.user = message;
    });

The header.html

<div class="header" ng-controller="GcUserCtrl as gcUserCtrl">
...
   <li><a ng-show="user" href="#">User: {{user.name}}</a></li>

2) establish a $rootScope variable

From my understanding, $rootScope serves as the root of all scopes and all $scope can access it.

The auth.js

$rootScope.user=user;

The heaeder.html (no controller necessary here)

<div class="header">
...
   <li><a ng-show="user" href="#">User: {{user.name}}</a></li>

So, what is the correct approach to handle this situation?

The first option seems somewhat resource-intensive due to the necessity for multiple checks during broadcast.
As for the second option, I'm not particularly fond of using global variables.

EDIT

3) employ a service

In response to alex's comment, I have included this alternative, although I haven't been able to get it functioning properly yet. (Here is the Plunker) It doesn't work without events being triggered

index.html

...
 <ng-include src="'header.html'"></ng-include>
...

header.html

Answer №1

To ensure user information is stored securely, it is recommended to utilize a dedicated Service for this purpose. This Service should be integrated with the authentication process to attach user data seamlessly. For effective authentication practices, consider implementing a Login Factory that handles the authentication and authorization tasks efficiently. By injecting the login Service into the factory, you can streamline the authentication process.

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

app.service('SessionService', function () {
  this.attachUser = function(userId, fName){
    this.userId = userId;
    this.fName = fName;
  }
});


app.controller('MainCtrl', function($scope, SessionService){
  // Ensure proper invocation of attachUser method upon authentication
  SessionService.attachUser(1234, 'John');

  $scope.userName = SessionService.fName; 
});

This code snippet exemplifies how to create a reliable Session handling Service in AngularJS. The MainCtrl controller accesses the properties of SessionService through dependency injection. Typically, the

SessionService.attachUser(userId, fName)

operation would reside within a specialized login factory.

Adopting this approach enhances application modularity by isolating session management responsibilities. Maintaining user sessions in a designated Service ensures better organization and scalability. This eliminates the need to search for global variables scattered throughout the codebase, such as $rootScope instances.

EDIT: Check out an updated plunker utilizing rootScope broadcast/on for change capture.

Answer 2

To ensure user information is stored securely, it is recommended to utilize a dedicated Service for this purpose. This Service should be integrated with the authentication process to attach user data seamlessly. For effective authentication practices, consider implementing a Login Factory that handles the authentication and authorization tasks efficiently. By injecting the login Service into the factory, you can streamline the authentication process.

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

app.service('SessionService', function () {
  this.attachUser = function(userId, fName){
    this.userId = userId;
    this.fName = fName;
  }
});


app.controller('MainCtrl', function($scope, SessionService){
  // Ensure proper invocation of attachUser method upon authentication
  SessionService.attachUser(1234, 'John');

  $scope.userName = SessionService.fName; 
});

This code snippet exemplifies how to create a reliable Session handling Service in AngularJS. The MainCtrl controller accesses the properties of SessionService through dependency injection. Typically, the

SessionService.attachUser(userId, fName)

operation would reside within a specialized login factory.

Adopting this approach enhances application modularity by isolating session management responsibilities. Maintaining user sessions in a designated Service ensures better organization and scalability. This eliminates the need to search for global variables scattered throughout the codebase, such as $rootScope instances.

EDIT: Check out an updated plunker utilizing rootScope broadcast/on for change capture.

Answer 3

Answer №2

Events serve as the primary method for indicating that some action must be taken by another entity. They signify that an action has occurred which may be of interest to another entity. Additionally, using events helps reduce scope pollution, as you've pointed out.

The statement regarding utilizing a service in this scenario is only partially correct. It is recommended that all login-related logic be encapsulated within a dedicated service specifically designed for handling logging in and out processes. This service would then trigger the event when a user logs in.

module.service('LoginHelper', function($rootScope) {
    this.loginUser = function(username, password) {
        // handle successful login
        $rootScope.broadcast('loggedIn', logginUserData)
    }
    this.logout = function() {
        // handle successful logout
        $rootScope.broadcast('loggedOut')
    }
})

The logged-in user data should be stored and managed by the service.

Alternatively, one could use $emit on $rootScope. While this limits the ability to listen for the 'loggedIn' event only on $rootScope, it does involve slightly less overhead.

Answer 4

Events serve as the primary method for indicating that some action must be taken by another entity. They signify that an action has occurred which may be of interest to another entity. Additionally, using events helps reduce scope pollution, as you've pointed out.

The statement regarding utilizing a service in this scenario is only partially correct. It is recommended that all login-related logic be encapsulated within a dedicated service specifically designed for handling logging in and out processes. This service would then trigger the event when a user logs in.

module.service('LoginHelper', function($rootScope) {
    this.loginUser = function(username, password) {
        // handle successful login
        $rootScope.broadcast('loggedIn', logginUserData)
    }
    this.logout = function() {
        // handle successful logout
        $rootScope.broadcast('loggedOut')
    }
})

The logged-in user data should be stored and managed by the service.

Alternatively, one could use $emit on $rootScope. While this limits the ability to listen for the 'loggedIn' event only on $rootScope, it does involve slightly less overhead.

Answer 5

Answer №3

Avoid using watches

One possible solution for this requirement would be to utilize an event mechanism, as suggested by alex. You can refer to a plunk demonstrating an example here: http://plnkr.co/edit/v6OXjOXZzF9McMvtn6hG?p=preview

However, in this specific scenario, it might not be ideal to follow the typical "angular way". Considering how $broadcast and/or $emit functions operate in AngularJS, which trigger listeners up or down the scope hierarchy, it's advisable to avoid them. You can read more about this in the documentation. Instead, other event propagation mechanisms could be considered based on the requirements.

app.controller('MainCtrl', function($scope, SessionService, $document){
  // Invoke attachUser differently (e.g., during authentication) - this is for testing purposes only
  $scope.isLoggedIn = false;
  $document.bind('$loggedin', function(){
      $scope.isLoggedIn = true;
      $scope.user = SessionService.fName;
  });
  $scope.logout = function() {
    SessionService.attachUser(null, null);
    $scope.isLoggedIn = false;
  };
});

app.controller('LoginCtrl', function($scope, SessionService, $document){
  $scope.doLogin = function() {
    console.log('doLogin');
    SessionService.attachUser(1234, $scope.username);  
    var doc = $document[0];
    var evt = new Event('$loggedin');
    doc.dispatchEvent(evt);
  };
});

For cleanup after the view is no longer needed, handle the $destroy event on the controller's scope and unbind the event handler...

$scope.$on('$destroy', function() {
    $document.unbind('$loggedin');
};

Refer to MDN for more information on triggering events using the DOM.

Update: [24 Sep]

A directive setup has been provided below, illustrating the concept:

app.directive('ngNest', function($parse, $compile, $timeout){
  // Directive code goes here
});

Further details and implementation of this directive can be found at: https://gist.github.com/deostroll/a9a2de04d3913f021f13

The results obtained from running this code are displayed below:

Live reload enabled.
$broadcast 1443074421928
$myEvt 14 1443074421929
$myEvt 19 1443074421930
DOM 1443074426405
$myEvt 14 1443074426405
$myEvt 19 1443074426405

It's worth noting the difference in timestamps when utilizing $broadcast. By broadcasting on $rootScope, Angular goes through the scope tree depth-first and triggers listeners attached to respective scopes in that order. This behavior is also validated within the source code for $emit and $broadcast methods.

Answer 6

Avoid using watches

One possible solution for this requirement would be to utilize an event mechanism, as suggested by alex. You can refer to a plunk demonstrating an example here: http://plnkr.co/edit/v6OXjOXZzF9McMvtn6hG?p=preview

However, in this specific scenario, it might not be ideal to follow the typical "angular way". Considering how $broadcast and/or $emit functions operate in AngularJS, which trigger listeners up or down the scope hierarchy, it's advisable to avoid them. You can read more about this in the documentation. Instead, other event propagation mechanisms could be considered based on the requirements.

app.controller('MainCtrl', function($scope, SessionService, $document){
  // Invoke attachUser differently (e.g., during authentication) - this is for testing purposes only
  $scope.isLoggedIn = false;
  $document.bind('$loggedin', function(){
      $scope.isLoggedIn = true;
      $scope.user = SessionService.fName;
  });
  $scope.logout = function() {
    SessionService.attachUser(null, null);
    $scope.isLoggedIn = false;
  };
});

app.controller('LoginCtrl', function($scope, SessionService, $document){
  $scope.doLogin = function() {
    console.log('doLogin');
    SessionService.attachUser(1234, $scope.username);  
    var doc = $document[0];
    var evt = new Event('$loggedin');
    doc.dispatchEvent(evt);
  };
});

For cleanup after the view is no longer needed, handle the $destroy event on the controller's scope and unbind the event handler...

$scope.$on('$destroy', function() {
    $document.unbind('$loggedin');
};

Refer to MDN for more information on triggering events using the DOM.

Update: [24 Sep]

A directive setup has been provided below, illustrating the concept:

app.directive('ngNest', function($parse, $compile, $timeout){
  // Directive code goes here
});

Further details and implementation of this directive can be found at: https://gist.github.com/deostroll/a9a2de04d3913f021f13

The results obtained from running this code are displayed below:

Live reload enabled.
$broadcast 1443074421928
$myEvt 14 1443074421929
$myEvt 19 1443074421930
DOM 1443074426405
$myEvt 14 1443074426405
$myEvt 19 1443074426405

It's worth noting the difference in timestamps when utilizing $broadcast. By broadcasting on $rootScope, Angular goes through the scope tree depth-first and triggers listeners attached to respective scopes in that order. This behavior is also validated within the source code for $emit and $broadcast methods.

Angular: Exploring the differences between $rootScope variable and event handling

Answer №1

Answer №2

Answer №3

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