InjectionToken

Use an InjectionToken whenever the type you are injecting is not reified (does not have a runtime representation) such as when injecting an interface, callable type, array or parametrized type.

InjectionToken is parameterized on T which is the type of object which will be returned by the Injector. This provides additional level of type safety.

interface MyInterface {...}
var myInterface = injector.get(new InjectionToken<MyInterface>('SomeToken'));
// myInterface is inferred to be MyInterface.

Example

Plain InjectionToken:

const BASE_URL = new InjectionToken<string>('BaseUrl');
const injector =
    Injector.create({providers: [{provide: BASE_URL, useValue: 'http://localhost'}]});
const url = injector.get(BASE_URL);
// here `url` is inferred to be `string` because `BASE_URL` is `InjectionToken<string>`.
expect(url).toBe('http://localhost');

Tree-shakable InjectionToken:

class MyService {
  constructor(readonly myDep: MyDep) {}
}

const MY_SERVICE_TOKEN = new InjectionToken<MyService>('Manually constructed MyService', {
  providedIn: 'root',
  factory: () => new MyService(inject(MyDep)),
});

const instance = injector.get(MY_SERVICE_TOKEN);
expect(instance instanceof MyService).toBeTruthy();
expect(instance.myDep instanceof MyDep).toBeTruthy();

Costructor parameters

InjectionToken<T>(
  _desc: string,
  options?: { providedIn?: Type<any> | 'root' | null; factory: () => T; },
);