anchor.diff:  <a id="ngStyle"></a>
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  -  ### NgStyle
  -
     ### NgStyle
   
     We can set inline styles dynamically, based on the state of the component.
  
positive.code:     要学习更多的*类似 index* 的值，例如`last`、`even`和`odd`，请参阅 [NgFor API 参考](../api/common/index/NgFor-directive.html)。
  
  :marked
    #### NgForTrackBy
  
    #### NgForTrackBy
  
    The `ngFor` directive has the potential to perform poorly, especially with large lists.
  
negative.code: :marked
    ### NgIf
  
    We can add an element subtree (an element and its children) to the DOM  by binding an `NgIf` directive to a #{_truthy} expression.
  
    通过绑定`NgIf`指令到真值表达式，可以把元素子树（元素及其子元素）添加到 DOM 上。
  