What can be the reason to use "controllerAs" property? - angularjs

Question

I am working on an AngularJS tutorial, and I see the following code:
.state('index',{
url:"/",
templateUrl:"views/index.html",
controller:"IndexCtrl",
controllerAs:"index"
})
What is the reason someone would want to use the controllerAs property?

Answer 1

Few things:
1. Reduce scope usage
Instead of loading every data in the scope of a controller, you could simply use this to load up everything that you require.
eg:
Route
state('index',{
url:"/",
templateUrl:"views/index.html",
controller:"ListCtrl",
controllerAs:"list"
})
In Controller
angular.module('feed').controller('ListCtrl', function($scope, reddit){
var vm = this;
vm.names = ["Michael", "Roy"];
});
In Template:
<ul>
<li ng-repeat="name in list.names">
<div>{{name}}</div>
</li>
</ul>
2. Correct scope usage
When multiple controllers come into play, scope becomes a tricky thing. Using controllerAs method will go a long way is resolving this. An example is shown below:
Wrong:
<span>Outside Controller: Your name is: {{username}}</span>
<div ng-controller="SignupController">
<span>Inside Controller: Your name is: {{username}}</span>
<fieldset legend="User details">
<input ng-model="username">
</fieldset>
</div>
Correct:
<span>Outside Controller: Your name is: {{user.name}}</span>
<div ng-controller="SignupController">
<span>Inside Controller: Your name is: {{user.name}}</span>
<fieldset legend="User details">
<input ng-model="user.name">
</fieldset>
</div>
Found an image which makes everthing more clear:
Courtesy : AngularJs "controller as" syntax - clarification?

Answer 2

Yes. A little more info:
Before the controllerAs syntax, methods and properties needed to be exposed to views by binding them to the $scope. With controllerAs, your controller instance is bound to the $scope as the property you select.
This way you can use Plain Old JavaScript Classes for your controllers.
Editorial: This is a much cleaner approach to development. One of the things that makes Angular so easy to write tests for is that your Controllers and components do not need to inherit from framework base-classes. See Backbone and Ember.
So with the old style your controllers would look like (in ES6 for simplicity):
YourController.$inject = ['$scope'];
class YourController {
constructor($scope) {
$scope.myMethod = () => { . . . };
$scope.myProperty = true;
}
}
With the controllerAs
class YourController {
constructor() {
this.myProperty = true;
}
myMethod() { . . . };
}
Just a plain old class rather than decorating or monkeypatching the $scope.

Answer 3

maybe you didn't googled enough!
http://toddmotto.com/digging-into-angulars-controller-as-syntax/
As the name "controllerAs" tell us, is an alias for controller them you can access your controller with that alias.

Answer 4

You can set your controller in many ways like :
$stateProvider.state('contacts', {
template: '<h1>{{title}}</h1>',
controller: function($scope){
$scope.title = 'My Contacts';
}
})
Or if you already have a controller defined on the module, like this:
$stateProvider.state('contacts', {
template: ...,
controller: 'ContactsCtrl'
})
Alternatively using the controllerAs syntax the above become:
$stateProvider.state('contacts', {
template: '<h1>{{contact.title}}</h1>',
controller: function(){
this.title = 'My Contacts';
},
controllerAs: 'contact'
})
and
$stateProvider.state('contacts', {
template: ...,
controller: 'ContactsCtrl as contact'
})
Or for more advanced needs you can use the controllerProvider to dynamically return a controller function or string for you:
$stateProvider.state('contacts', {
template: ...,
controllerProvider: function($stateParams) {
var ctrlName = $stateParams.type + "Controller";
return ctrlName;
}
})
Source : https://github.com/angular-ui/ui-router/wiki#controllers
Simply, Controller as syntax helps when we are working with nested controllers. The named scopes are clearly defined so there won’t be conflicts between controllers since you must state which controller you’re referencing before the dot.
<div ng-controller="Shell as shellVm">
<h1>{{shellVm.title}}</h1>
<article ng-controller="Customers as customersVm">
<h2>{{customersVm.title}} in {{shellVm.title}}</h2>
<ul ng-repeat="c in customersVm.customers">
<li>{{c.name}}</li>
</ul>
</article>
</div>
Refer AngularJs "controller as" syntax - clarification? as well.