Route Resolve Promises (Y081)

https://github.com/johnpapa/angularjs-styleguide/edit/master/README.md
- When a controller depends on a promise to be resolved before the controller is activated, resolve those dependencies in the `$routeProvider` before the controller logic is executed. If you need to conditionally cancel a route before the controller is activated, use a route resolver.
- Use a route resolve when you want to decide to cancel the route before ever transitioning to the View.

_Why?_: A controller may require data before it loads. That data may come from a promise via a custom factory or [$http](https://docs.angularjs.org/api/ng/service/$http). Using a [route resolve](https://docs.angularjs.org/api/ngRoute/provider/$routeProvider) allows the promise to resolve before the controller logic executes, so it might take action based on that data from the promise.

_Why?_: The code executes after the route and in the controller’s activate function. The View starts to load right away. Data binding kicks in when the activate promise resolves. A “busy” animation can be shown during the view transition (via ng-view or ui-view)

Note: The code executes before the route via a promise. Rejecting the promise cancels the route. Resolve makes the new view wait for the route to resolve. A “busy” animation can be shown before the resolve and through the view transition. If you want to get to the View faster and do not require a checkpoint to decide if you can get to the View, consider the [controller `activate` technique](#style-y080) instead.

``` javascript
/* avoid */
angular
.module('app')
.controller('Avengers', Avengers);

function Avengers(movieService) {
var vm = this;
// unresolved
vm.movies;
// resolved asynchronously
movieService.getMovies().then(function(response) {
vm.movies = response.movies;
});
}
```

``` javascript
/* better */

// route-config.js
angular
.module('app')
.config(config);

function config($routeProvider) {
$routeProvider
.when('/avengers', {
templateUrl: 'avengers.html',
controller: 'Avengers',
controllerAs: 'vm',
resolve: {
moviesPrepService: function(movieService) {
return movieService.getMovies();
}
}
});
}

// avengers.js
angular
.module('app')
.controller('Avengers', Avengers);

Avengers.$inject = ['moviesPrepService'];
function Avengers(moviesPrepService) {
var vm = this;
vm.movies = moviesPrepService.movies;
}
```

Note: The example below shows the route resolve points to a named function, which is easier to debug and easier to handle dependency injection.

``` javascript
/* even better */

// route-config.js
angular
.module('app')
.config(config);

function config($routeProvider) {
$routeProvider
.when('/avengers', {
templateUrl: 'avengers.html',
controller: 'Avengers',
controllerAs: 'vm',
resolve: {
moviesPrepService: moviesPrepService
}
});
}

function moviePrepService(movieService) {
return movieService.getMovies();
}

// avengers.js
angular
.module('app')
.controller('Avengers', Avengers);

Avengers.$inject = ['moviesPrepService'];
function Avengers(moviesPrepService) {
var vm = this;
vm.movies = moviesPrepService.movies;
}
```

Note: The code example's dependency on `movieService` is not minification safe on its own. For details on how to make this code minification safe, see the sections on [dependency injection](#manual-annotating-for-dependency-injection) and on [minification and annotation](#minification-and-annotation).