anchor.diff:    The companion component class provides heroes, adds heroes into the array, and can reset the array.
   
     和模板相伴的组件类可以提供英雄数组，能把新的英雄添加到数组中，还能重置英雄数组。
  +  
   +makeExample('pipes/ts/src/app/flying-heroes.component.ts', 'v1', 'src/app/flying-heroes.component.ts (v1)')(format='.')
   
   :marked
  
positive.code: :marked
    A breakpoint on the pipe's request for data shows the following:
    
    * Each binding gets its own pipe instance.
    * Each pipe instance caches its own URL and data.
    * Each pipe instance only calls the server once.
  
    ### *JsonPipe*
  
  
negative.code:   来看看我们是如何添加新英雄的：
  
  +makeExample('pipes/ts/src/app/flying-heroes.component.ts', 'push')(format='.')
  
  :marked
    You add the hero into the `heroes` array.  The reference to the array hasn't changed.
    It's the same array. That's all Angular cares about. From its perspective, *same array, no change, no display update*.
  