angular - Is it possible to inject interface with angular2?

Question

i wonder if there is a proper way to inject interfaces in Angular2? (cf. below)

I think this is related with the missing @Injectable() decorator on the interface, but it seems this is not allowed.

Regards.

When CoursesServiceInterface is implemented as an interface, the TypeScript compiler complains "CoursesServiceInterface cannot find name":

import {CoursesServiceInterface} from './CoursesService.interface';
import {CoursesService} from './CoursesService.service';
import {CoursesServiceMock} from './CoursesServiceMock.service';
bootstrap(AppComponent, [
  ROUTER_PROVIDERS, 
  GlobalService,
  provide(CoursesServiceInterface, { useClass: CoursesServiceMock })
  ]);

but with CoursesServiceInterface as an interface:

import {Injectable} from 'angular2/core';
import {Course} from './Course.class';
//@Injectable()
export interface CoursesServiceInterface {
    getAllCourses(): Promise<Course[]>;//{ return null; };
    getCourse(id: number): Promise<Course>;// { return null; };
    remove(id: number): Promise<{}>;// { return null; };
}

When service is a class, the TypeScript compiler doesn't complain anymore:

import {Injectable} from 'angular2/core';
import {Course} from './Course.class';
@Injectable()
export class CoursesServiceInterface {  
    getAllCourses() : Promise<Course[]> { return null; };
    getCourse(id: number) :Promise<Course> { return null; };
    remove (id: number) : Promise<{}> { return null; };
}

Answer 1

No, interfaces are not supported for DI. With TypeScript interfaces are not available at runtime anymore, only statically and therefore can't be used as DI tokens.

Alternatively you can use strings as keys or InjectionToken

provide('CoursesServiceInterface', {useClass: CoursesServiceMock}) // old

providers: [{provide: 'CoursesServiceInterface', useClass: CoursesServiceMock}]

and inject it like

constructor(@Inject('CoursesServiceInterface') private coursesService:CoursesServiceInterface) {}

See also https://angular.io/api/core/InjectionToken