anchor.diff:  a#extract-data
   :marked
     ## Process the response object
  +
     ## 处理Response响应对象
  +
     Remember that our `getHeroes()` method mapped the `#{_priv}http.get` response object to heroes with an `#{_priv}extractData` helper method:
     
     记住，`getHeroes()`借助一个`#{_priv}extractData`辅助方法来把`#{_priv}http.get`的响应对象映射成了英雄列表：
  
positive.code: .l-main-section
  :marked
    ## Appendix: Tour of Heroes in-memory server
    ## 附录：《英雄指南》的内存(in-memory)服务器
  
    If we only cared to retrieve data, we could tell Angular to get the heroes from a `heroes.json` file like this one:
    
    如果我们只关心获取到的数据，我们可以告诉Angular从一个从一个`heroes.json`文件中获取英雄列表，就像这样：
  +makeJson('server-communication/ts/app/heroes.json', null, 'app/heroes.json')(format=".")
  .l-sub-section
    :marked
  
negative.code:      并非所有服务器都会返回一个带`data`属性的对象。
  :marked
    ### Do not return the response object
  
    ### 不要返回响应(Response)对象
  
    Our `getHeroes()` could have returned the HTTP response. Bad idea! 
    The point of a data service is to hide the server interaction details from consumers.
    The component that calls the `HeroService` wants heroes. 
  