Optional

A constructor parameter decorator that marks a dependency as optional.

查看"说明"...

参见

说明

The DI framework provides null if the dependency is not found. For example, the following code allows the possibility of a null result:

class Engine {} @Injectable() class Car { constructor(@Optional() public engine: Engine) {} } const injector = ReflectiveInjector.resolveAndCreate([Car]); expect(injector.get(Car).engine).toBeNull();
      
      class Engine {}

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

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

选项