In an AngularJS module we can register object instances or recipes to create instances, then we can have them available through Dependency Injection.
We can register an object instance through the value method.
In the example, we register an object instance and we name it person. The name of a registered instance has to be unique in the module (it's basically a singleton).
When we declare mainController we can have our registered person object through Dependency Injection by simply specifying the name person as an argument of the controller function.