@ngdoc overview
@name Controllers
@description

# Understanding Controllers

In Angular, a Controller is a JavaScript **constructor function** that is used to augment the 
{@link scope Angular Scope}.

When a Controller is attached to the DOM via the {@link api/ng.directive:ngController ng-controller}
directive, Angular will instantiate a new Controller object, using the specified Controller's
**constructor function**.  A new **child scope** will be available as an injectable parameter to the
Controller's constructor function as `$scope`.

Use Controllers to:

- Set up the initial state of the `$scope` object.
- Add behavior to the `$scope` object.

# Setting up the initial state of a `$scope` object

Typically, when you create an application you need to set up the initial state for the Angular
`$scope`. You set up the initial state of a scope by attaching properties to the `$scope` object.
The properties contain the **view model** (the model that will be presented by the view).  All the
`$scope` properties will be available to the template at the point in the DOM where the Controller
is registered.

The following example shows a very simple constructor function for a Controller, `GreetingCtrl`,
which attaches a `greeting` property containing the string `'Hola!'` to the `$scope`:

```js
    function GreetingCtrl($scope) {
        $scope.greeting = 'Hola!';
    }
```

Once the Controller has been attached to the DOM, the `greeting` property can be data-bound to the
template:

```js
    <div ng-controller="GreetingCtrl">
      {{ greeting }}
    </div>
```

**NOTE**: Although Angular allows you to create Controller functions in the global scope, this is
not recommended.  In a real application you should use the `.controller` method of your
{@link module Angular Module} for your application as follows:

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

    myApp.controller('GreetingCtrl', ['$scope', function($scope) {
        $scope.greeting = 'Hola!';
    }]);
```

We have used an **inline injection annotation** to explicitly specify the dependency
of the Controller on the `$scope` service provided by Angular. See the guide on 
[Dependency Injection](http://docs.angularjs.org/guide/di) for more information.


# Adding Behavior to a Scope Object

In order to react to events or execute computation in the view we must provide behavior to the
scope. We add behavior to the scope by attaching methods to the `$scope` object.  These methods are
then available to be called from the template/view.

The following example uses a Controller to add a method to the scope, which doubles a number:

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

    myApp.controller('DoubleCtrl', ['$scope', function($scope) {
        $scope.double = function(value) { return value * 2; };
    }]);
```

Once the Controller has been attached to the DOM, the `double` method can be invoked in an Angular
expression in the template:

```js
    <div ng-controller="DoubleCtrl">
      Two times <input ng-model="num"> equals {{ double(num) }}
    </div>
```

As discussed in the {@link concepts Concepts} section of this guide, any
objects (or primitives) assigned to the scope become model properties. Any methods assigned to
the scope are available in the template/view, and can be invoked via angular expressions
and `ng` event handler directives (e.g. {@link api/ng.directive:ngClick ngClick}).

# Using Controllers Correctly

In general, a Controller shouldn't try to do too much. It should contain only the business logic
needed for a single view.

The most common way to keep Controllers slim is by encapsulating work that doesn't belong to
controllers into services and then using these services in Controllers via dependency injection.
This is discussed in the {@link di Dependency Injection} {@link dev_guide.services
Services} sections of this guide.

Do not use Controllers for:

- Any kind of DOM manipulation — Controllers should contain only business logic. DOM
manipulation (the presentation logic of an application) is well known for being hard to test.
Putting any presentation logic into Controllers significantly affects testability of the business
logic. Angular offers {@link databinding databinding} for automatic DOM manipulation. If
you have to perform your own manual DOM manipulation, encapsulate the presentation logic in
{@link guide/directive directives}.
- Input formatting — Use {@link forms angular form controls} instead.
- Output filtering — Use {@link filter angular filters} instead.
- Sharing stateless or stateful code across Controllers — Use {@link dev_guide.services angular
services} instead.
- Managing the life-cycle of other components (for example, to create service instances).


# Associating Controllers with Angular Scope Objects

You can associate Controllers with scope objects implicitly via the {@link api/ng.directive:ngController ngController
directive} or {@link api/ngRoute.$route $route service}.


## Simple Spicy Controller Example

To illustrate further how Controller components work in Angular, let's create a little app with the
following components:

- A {@link templates template} with two buttons and a simple message
- A model consisting of a string named `spice`
- A Controller with two functions that set the value of `spice`

The message in our template contains a binding to the `spice` model, which by default is set to the
string "very". Depending on which button is clicked, the `spice` model is set to `chili` or
`jalapeño`, and the message is automatically updated by data-binding.

<example module="spicyApp1">
  <file name="index.html">
    <div ng-app="spicyApp1" ng-controller="SpicyCtrl">
     <button ng-click="chiliSpicy()">Chili</button>
     <button ng-click="jalapenoSpicy()">Jalapeño</button>
     <p>The food is {{spice}} spicy!</p>
    </div>
  </file>
  <file name="app.js">
    var myApp = angular.module('spicyApp1', []);

    myApp.controller('SpicyCtrl', ['$scope', function($scope){
        $scope.spice = 'very';
        
        $scope.chiliSpicy = function() {
            $scope.spice = 'chili';
        };
        
        $scope.jalapenoSpicy = function() {
            $scope.spice = 'jalapeño';
        };
    }]);
  </file>
</example>

Things to notice in the example above:

- The `ng-controller` directive is used to (implicitly) create a scope for our template, and the
scope is augmented (managed) by the `SpicyCtrl` Controller.
- `SpicyCtrl` is just a plain JavaScript function. As an (optional) naming convention the name
starts with capital letter and ends with "Ctrl" or "Controller".
- Assigning a property to `$scope` creates or updates the model.
- Controller methods can be created through direct assignment to scope (see the `chiliSpicy` method)
- The Controller methods and properties are available in the template (for the `<div>` element and
its children).

## Spicy Arguments Example

Controller methods can also take arguments, as demonstrated in the following variation of the
previous example.

<example module="spicyApp2">
  <file name="index.html">
  <div ng-app="spicyApp2" ng-controller="SpicyCtrl">
   <input ng-model="customSpice">
   <button ng-click="spicy('chili')">Chili</button>
   <button ng-click="spicy(customSpice)">Custom spice</button>
   <p>The food is {{spice}} spicy!</p>
  </div>
  </file>
  <file name="app.js">
    var myApp = angular.module('spicyApp2', []);

    myApp.controller('SpicyCtrl', ['$scope', function($scope){
        $scope.customSpice = "wasabi";
        $scope.spice = 'very';
        
        $scope.spicy = function(spice){
            $scope.spice = spice;
        };
    }]);
  </file>
</example>

Notice that the `SpicyCtrl` Controller now defines just one method called `spicy`, which takes one
argument called `spice`. The template then refers to this Controller method and passes in a string
constant `'chili'` in the binding for the first button and a model property `customSpice` (bound to an
input box) in the second button.

## Scope Inheritance Example

It is common to attach Controllers at different levels of the DOM hierarchy.  Since the 
{@link api/ng.directive:ngController ng-controller} directive creates a new child scope, we get a
hierarchy of scopes that inherit from each other.  The `$scope` that each Controller receives will
have access to properties and methods defined by Controllers higher up the hierarchy.
See [Understanding Scopes](https://github.com/angular/angular.js/wiki/Understanding-Scopes) for
more information about scope inheritance.

<example module="scopeInheritance">
  <file name="index.html">
    <div ng-app="scopeInheritance" class="spicy">
      <div ng-controller="MainCtrl">
        <p>Good {{timeOfDay}}, {{name}}!</p>

        <div ng-controller="ChildCtrl">
          <p>Good {{timeOfDay}}, {{name}}!</p>

          <div ng-controller="GrandChildCtrl">
            <p>Good {{timeOfDay}}, {{name}}!</p>
          </div>
        </div>
      </div>
    </div>
  </file>
  <file name="app.css">
    div.spicy div {
      padding: 10px;
      border: solid 2px blue;
    }
  </file>
  <file name="app.js">
      var myApp = angular.module('scopeInheritance', []);
      myApp.controller('MainCtrl', ['$scope', function($scope){
        $scope.timeOfDay = 'morning';
        $scope.name = 'Nikki';
      }]);
      myApp.controller('ChildCtrl', ['$scope', function($scope){
        $scope.name = 'Mattie';
      }]);
      myApp.controller('GrandChildCtrl', ['$scope', function($scope){
        $scope.timeOfDay = 'evening';
        $scope.name = 'Gingerbreak Baby';
      }]);
  </file>
</example>

Notice how we nested three `ng-controller` directives in our template. This will result in four
scopes being created for our view:

- The root scope
- The `MainCtrl` scope, which contains `timeOfDay` and `name` properties
- The `ChildCtrl` scope, which inherits the `timeOfDay` property but overrides (hides) the `name`
property from the previous
- The `GrandChildCtrl` scope, which overrides (hides) both the `timeOfDay` property defined in `MainCtrl`
and the `name` property defined in `ChildCtrl`

Inheritance works with methods in the same way as it does with properties. So in our previous
examples, all of the properties could be replaced with methods that return string values.


## Testing Controllers

Although there are many ways to test a Controller, one of the best conventions, shown below,
involves injecting the {@link api/ng.$rootScope $rootScope} and {@link api/ng.$controller $controller}:

**Controller Definition:**
```js
    var myApp = angular.module('myApp',[]);

    myApp.controller('MyController', function($scope) {
      $scope.spices = [{"name":"pasilla", "spiciness":"mild"},
                       {"name":"jalapeno", "spiceiness":"hot hot hot!"},
                       {"name":"habanero", "spiceness":"LAVA HOT!!"}];
      $scope.spice = "habanero";
    });
```

**Controller Test:**
```js
describe('myController function', function() {

  describe('myController', function() {
    var $scope;

    beforeEach(module('myApp'));

    beforeEach(inject(function($rootScope, $controller) {
      $scope = $rootScope.$new();
      $controller('MyController', {$scope: $scope});
    }));

    it('should create "spices" model with 3 spices', function() {
      expect($scope.spices.length).toBe(3);
    });

    it('should set the default value of spice', function() {
      expect($scope.spice).toBe('habanero');
    });
  });
});
```


If you need to test a nested Controller you need to create the same scope hierarchy
in your test that exists in the DOM:

```js
describe('state', function() {
    var mainScope, childScope, grandChildScope;

    beforeEach(module('myApp'));

    beforeEach(inject(function($rootScope, $controller) {
        mainScope = $rootScope.$new();
        $controller('MainCtrl', {$scope: mainScope});
        childScope = mainScope.$new();
        $controller('ChildCtrl', {$scope: childScope});
        grandChildScope = childScope.$new();
        $controller('GrandChildCtrl', {$scope: grandChildScope});
    }));

    it('should have over and selected', function() {
        expect(mainScope.timeOfDay).toBe('morning');
        expect(mainScope.name).toBe('Nikki');
        expect(childScope.timeOfDay).toBe('morning');
        expect(childScope.name).toBe('Mattie');
        expect(grandChildScope.timeOfDay).toBe('evening');
        expect(grandChildScope.name).toBe('Gingerbreak Baby');
    });
});
```