Optional

What it does

A parameter metadata that marks a dependency as optional. Injector provides null if the dependency is not found.

How to use

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

Description

For more details, see the Dependency Injection Guide.

Example

class Engine {}

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

const injector = ReflectiveInjector.resolveAndCreate([Car]);
expect(injector.get(Car).engine).toBeNull();