Can factory provider have optional dependencies?

Question

For example:

@NgModule ({
  providers: [ 
    { provide: MyService, 
      useFactory: (optionalDep) => new MyService(optionalDep)
      deps: [SOME_DEP]
    }
})
class MyModule {}

Can useFactory have optional dependencies?

Answer 1

According to official doc, you can do the following:

const Location = new InjectionToken('location');
const Hash = new InjectionToken('hash');

const injector = Injector.create([{
  provide: Hash,
  useFactory: (location: string) => `Hash for: ${location}`,
  // use a nested array to define metadata for dependencies.
  deps: [[new Optional(), Location]]
}]);

expect(injector.get(Hash)).toEqual('Hash for: null');

See https://angular.io/api/core/FactoryProvider#example for more

Answer 2

I have found such a workaround:

class OptionalDepHolder {
  constructor(@Optional() @Inject(SOME_DEP) public optionalDep) {}
}

@NgModule ({
  providers: [ 
    { provide: MyService, 
      useFactory: (holder) => new MyService(holder.optionalDep)
      deps: [OptionalDepHolder]
    }
})
class MyModule {}