angular-cn/public/docs/js/latest/api/di/OptionalAnnotation-class.jade
2015-06-01 23:18:32 -07:00

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p.location-badge.
exported from <a href='../di'>angular2/di</a>
defined in <a href="https://github.com/angular/angular/tree/master/modules/angular2/src/di/annotations_impl.ts#L54-L72">angular2/src/di/annotations_impl.ts (line 54)</a>
:markdown
A parameter annotation that marks a dependency as optional. <a href='Injector-class.html'><code>Injector</code></a> provides `null` if
the dependency is not found.
```
class AComponent {
constructor(@Optional() aService:MyService) {
this.aService = aService;
}
}
```