anchor.diff:    fact `InjectableMetadata` #{_decorator}s that
     identify a class as a target for instantiation by an injector.
   
  +  我们**可以**添加它。但是它不是必需的，因为`HerosComponent`已经有`@Component`装饰器了，这个装饰器类（和我们随后将会学到的`@Directive`和`@Pipe`一样）是<a href="#{injMetaUrl}">InjectableMetadata</a>的子类型。实际上，这个`InjectableMetadata`装饰器是把一个类标识为注入器实例化的目标。
  +
   block ts-any-decorator-will-do
     .l-sub-section
       :marked
         At runtime, injectors can read class metadata in the transpiled JavaScript code
         and use the constructor parameter type information
  -      to determine what things to inject. 
  +      to determine what things to inject.
  +
  +      在运行时，注入器可以从编译后的JavaScript代码中读取类的元数据，并使用构造函数的参数类型信息来决定注入什么。 
   
         Not every JavaScript class has metadata.
         The TypeScript compiler discards metadata by default.
  
positive.code:   ### 在组件中注册提供商
  
    Here's a revised `HeroesComponent` that registers the `HeroService`.
  
  +makeExample('dependency-injection/ts/app/heroes/heroes.component.1.ts', 'full','app/heroes/heroes.component.ts', stylePattern)(format='.')
  
  
negative.code: :marked
    ### The *Provider* class !{__andProvideFn}
  
    ### *Provider*类和*provide*对象常量
  :marked
    We wrote the `providers` #{_array} like this:
  
  