Use services to communicate with a server.

Services

Well done! The `city_name` now shows up in the view. How does it work?
1. First in **js/services/forecast.js**, we made a new _service_. We used `app.factory` to create a new service named `forecast`
2. The `forecast` service needs to use AngularJS's built-in `$http` to fetch JSON from the server. Therefore, we add `$http` to the `forecast` service as a dependency, like this:
    ```javascript
    ['$http', function($http) {
      // ...
    }]
    ```
    Now `$http` is available to use inside `forecast`.
3. Then, inside `forecast`, we use `$http` to construct an HTTP `GET` request for the weather data. If the request succeeds, the weather data is returned; otherwise the error info is returned.
4. Next in the controller, we used the `forecast` service to fetch data from the server. First we added `forecast` into `MainController` as a dependency so that it's available to use. Then within the controller we used `forecast` to asynchronously fetch the weather data from the server and store it into `$scope.fiveDay`
5. As before, any properties attached to `$scope` become available to use in the view. This means in **index.html**, we can display the `city_name` using an expression as done before.


Services II

So far we've made AngularJS apps by adding data to a controller, and then displaying it in a view.

But what happens when the data contains hundreds of items, or if it's constantly changing like weather or financial data? Hardcoding data into a controller won't work anymore.

A better solution is to read the live data from a server. We can do this by creating a _service_.


Services I

Why are services useful?  Instead of filling the controller with code to fetch weather data from a server, it's better to move this independent logic into a service so that it can be reused by other parts of the app.

What can we generalize so far?
* Directives are a way to make standalone UI components, like `<app-info>`
* Services are a way to make standalone communication logic, like `forecast` which fetches weather data from a server
