Angular Component的职责：

Ideally, a component’s job is to enable the user experience and nothing more. A component should present properties and methods for data binding, in order to mediate between the view (rendered by the template) and the application logic (which often includes some notion of a model).

理想情况下，Angular Component唯一的职责就是提供user experience，除此别无其他。一个Component应当包含properties和方法，用于数据绑定，以及作为视图(通过模板渲染而成)和应用逻辑之间沟通的渠道。

Angular Service

通过@Injectable()这个装饰器将一个class定义成Angular服务。

To define a class as a service in Angular, use the @Injectable() decorator to provide the metadata that allows Angular to inject it into a component as a dependency.