Advanced topics

Controlling visibility

You can be more specific where you want to get dependencies from. For instance, you can ask for another directive on the same element.

class CustomInputComponent {
  constructor(@Self() f: FormatterDirective) {}
}

Or you can ask for a directive in the same template, that is, you can only inject an ancestor directive from the same HTML file.

class CustomInputComponent {
  constructor(@Host() f: CustomForm) {}
}

Finally, you can ask to skip the current element, which can be handy for decorating existing providers or building up tree-like structures.

class SomeComponent {
  constructor(@SKipSelf() ancestor: SomeComponent) {}
}

Optional dependencies

To mark a dependency as optional, use the Optional decorator.

class Login {
  constructor(@Optional() service: LoginService) {}
}

 

More on registering providers

Passing a class into an array of providers is the same as using a provider with useClass, that is, the following two examples are identical:

@NgModule({
providers...