anchor.diff:  
     1. We add a constructor that also defines a private property.
   
  -  1. 我们添加了一个构造函数，同时还定义了一个私有属性。
  +     添加一个构造函数，并定义一个私有属性。
   
     1. We add to the component's `providers` metadata.
   
  -  1. 我们添加了组件的`providers`元数据
  +     添加组件的`providers`元数据。
   
     Here's the constructor:
   
  
positive.code: :marked
    Ask for heroes and they are there in the returned result.
  
    请求英雄数据，并直接在结果中返回它。
  
    Someday we're going to get heroes from a remote server. We don’t call http yet, but we aspire to in later chapters.
  
    将来，我们会从远端服务器上获取英雄数据。我们还没调用http，但在未来的章节中我们会希望这么做。
  
    When we do, we'll have to wait for the server to respond and we won't be able to block the UI while we wait,
    even if we want to (which we shouldn't) because the browser won't block.
  
    那时候，我们不得不等待服务器返回，并且在等待时，我们没法阻塞UI响应，即使我们想这么做（也不应这么做）也做不到，因为浏览器不会阻塞。
  
    We'll have to use some kind of asynchronous technique and that will change the signature of our `getHeroes` method.
  
  
negative.code: 
    We pass our callback function as an argument to the !{_Promise}'s **then** method:
  
    我们把回调函数作为参数传给承诺对象的**then**方法：
  
  +makeExample('toh-4/ts/app/app.component.ts', 'get-heroes', 'app/app.component.ts (getHeroes - revised)')(format=".")
  
  