Parameter decorator to be used on constructor parameters, which marks the parameter as being an optional dependency. The DI framework provides null if the dependency is not found.

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See also

• "Dependency Injection Guide".

Description

Can be used together with other parameter decorators that modify how dependency injection operates.

Options

Usage notes

The following code allows the possibility of a null result:

class Engine {}

@Injectable()
class Car {
  constructor(@Optional() public engine: Engine) {}
}

const injector =
    Injector.create({providers: [{provide: Car, deps: [[new Optional(), Engine]]}]});
expect(injector.get(Car).engine).toBeNull();