@ngdoc error
@name $injector:unpr
@fullName Unknown Provider
@description

This error results from the `$injector` being unable to resolve a required
dependency. To fix this, make sure the dependency is defined and spelled
correctly. For example:

```
angular.module('myApp', [])
  .controller('MyController', ['myService', function (myService) {
    // Do something with myService
  }]);
```

The above code will fail with `$injector:unpr` if `myService` is not defined.

Making sure each dependency is defined will fix the problem, as noted below.

```
angular.module('myApp', [])
  .service('myService', function () { /* ... */ })
  .controller('MyController', ['myService', function (myService) {
    // Do something with myService
  }]);
```

An unknown provider error can also be caused by accidentally redefining a
module using the `angular.module` API, as shown in the following example.

```
angular.module('myModule', [])
  .service('myCoolService', function () { /* ... */ });

angular.module('myModule', [])
  // myModule has already been created! This is not what you want!
  .directive('myDirective', ['myCoolService', function (myCoolService) {
    // This directive definition throws unknown provider, because myCoolService
    // has been destroyed.
  }]);
```

To fix this problem, make sure you only define each module with the
`angular.module(name, [requires])` syntax once across your entire project.
Retrieve it for subsequent use with `angular.module(name)`. The fixed example
is shown below.

```
angular.module('myModule', [])
  .service('myCoolService', function () { /* ... */ });

angular.module('myModule')
  .directive('myDirective', ['myCoolService', function (myCoolService) {
    // This directive definition does not throw unknown provider.
  }]);
```


Attempting to inject one controller into another will also throw an `Unknown provider` error:

```
angular.module('myModule', [])
  .controller('MyFirstController', function() { /* ... */ })
  .controller('MySecondController', ['MyFirstController', function(MyFirstController) {
    // This controller throws an unknown provider error because
    // MyFirstController cannot be injected.
  }]);
```

Use the `$controller` service if you want to instantiate controllers yourself.

Attempting to inject a scope object into anything that's not a controller or a directive,
for example a service, will also throw an `Unknown provider: $scopeProvider <- $scope` error.
This might happen if one mistakenly registers a controller as a service, ex.:

```
angular.module('myModule', [])
  .service('MyController', ['$scope', function($scope) {
    // This controller throws an unknown provider error because
    // a scope object cannot be injected into a service.
  }]);
```
