angular-docs-cn/public/docs/js/latest/api/di_annotations/Optional-class.jade

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  exported from <a href="/angular2/di_annotations.html">angular2/di_annotations</a>
  defined in <a href="https://github.com/angular/angular/tree/master/modules/angular2/src/di/annotations.js#L77">angular2/src/di/annotations.js (line 77)</a>

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  A parameter annotation that marks a dependency as optional. <a href="../di/Injector-class.html"><code>Injector</code></a> provides `null` if the dependency is not
  found.
  
  ```
  class AComponent {
    constructor(@Optional() aService:MyService) {
      this.aService = aService;
    }
  }
  ```
  
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