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Why You Should Use AngularJS's "Controller as" Syntax

Published Mar 30, 2017Last updated Nov 02, 2019
Why You Should Use AngularJS's "Controller as" Syntax

What is this "Controller as" syntax?

AngularJS has become a popular front-end framework, which is why you've probably heard the term "controller as" thrown around a bit. This syntax is a way for us to access properties and methods of a controller declared on the controller via this. The support for this was introduced in AngularJS version 1.1.5.

Why should you use it?

Here are a few very good reasons:

  • When using nested scopes, it becomes completely clear where a method or property reference belongs to.
  • By not using $parent to access the properties of a parent controller, if things get moved, we can still be sure we are referencing the correct controller.
  • Because we are using dot notation, it becomes impossible to two-way bind to a primitive.

Example of NOT USING the "controller as" syntax

By not using the "Controller as" syntax, we can see things get complicated pretty quickly (imagine this in a very large application):

<div ng-app="app" ng-controller="SiteController">

  <!-- we are pretty sure we are getting the title from the SiteController -->
  <h1>{{title}}</h1>
    
    <div ng-controller="PersonController">
       
        <!-- is this the title from SiteController or PersonController? 
        is there even a title in both? -->
        <h2>{{title}}</h2>
        
    	<div ng-repeat="person in PersonCtrl.people">
        
        	<span>{{person.name}}</span>
            
      	</div>
    
    </div>

</div>

Example of USING the "controller as" syntax

To use our "Controller as" syntax, first, we declare all of our properties and methods on the this property of our controller:

// site.controller.js:
(function() {

  'use strict';

  angular.module('app').controller('SiteController', SiteController);

  // no need to inject $scope because we don't need it
  SiteController.$inject = [];

  function SiteController() {
        
        // assigning this to a loacal variable makes it easier to 
        // declare properties and methods in the controller
    	var vm = this;
        
        // declare our title on this
        vm.title = "Welcome!";

  }

})();

// other.controller.js:
(function() {

  'use strict';

  angular.module('app').controller('OtherController', OtherController);

  function OtherController() {
   
    	var vm = this;
        
        vm.title = "Other title!";

  }

})();

Then things become a lot more visibile in the view. We can see where each bit of data is coming from:

<div ng-app="app" ng-controller="SiteController as SiteCtrl">

    <!-- we can be sure we are getting the title from the SiteController -->
  <h1>{{SiteCtrl.title}}</h1>
    
    <div ng-controller="OtherController as OtherCtrl">
       
        <!-- we can be sure we are getting the title from the OtherCtrl -->
        <h2>{{OtherCtrl.title}}</h2>
    
    </div>

</div>

Here is a codepen to illustrate that.

Happy coding 🎉

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post comments3Replies
Paul McClean
6 years ago

This is great Christopher, thanks for the steer

Jiran Cao
6 years ago

Hi Christopher, this is a very great guide.

However the link “AngularJS Directives: A Beginner’s Practical Guide” is invalid, would you mind providing the valid link for it?

Thanks for your help.

---- Jiran

Christopher Northfield
5 years ago

Thanks Jiran, that link has been removed as there is no permanent source.