typescript dependency injection in super()

Question

I have a class called restService like bellow:

@Injectable({
  providedIn: 'root'
})
export class RestService {

  private baseUrl: string;

  constructor(private http: HttpClient) {
    this.baseUrl = environment.jsonServerUrl;
  }
}

and I have another class extends RestService class called UploaderService like this:

@Injectable({
  providedIn: 'root'
})
export class UploaderService extends RestService {

  constructor() {
    super(); // error occurred here!
  }
}

but when I write super method error occurred because RestService Class has Dependency Injection in its constructor, and I don't know how can I inject that in the super. How can I fix that?

If the constructor in UploaderService does nothing, you could drop it altogether. — Martin Parenteau
– Martin Parenteau, Commented Oct 8, 2019 at 13:45

Pac0 · Accepted Answer · 2019-10-08 14:52:51Z

You can repeat the parameters, as shown in other answers.

There is another way, though, which is handy when you have many parameters and extended classes : use Injector to get the dependencies in the base class.

Then, you only need to repeat the "Injector" injection in derived classes, which can save a lot of space and mind sanity when you have many services to inject in base class, but not a lot in derived class.

import { MyService } from './my.service';
import { FooService } from './foo.service';
import { Injector } from '@angular/core';

export class Base {
    protected myService: MyService;
    protected fooService: FooService;

  constructor (protected injector: Injector) {
    this.myService = injector.get(MyService);
    this.fooService = injector.get(FooService);
  }
}

export class Derived extends Base {
  constructor(protected injector: Injector) {
    super(injector);
  }
}

JonasMH · Accepted Answer · 2019-10-08 13:25:10Z

5

You need to pass through the injection

@Injectable({
  providedIn: 'root'
})
export class UploaderService extends RestService {

  constructor(http: HttpClient) {
    super(http);
  }
}

answered Oct 8, 2019 at 13:25

JonasMH

1,18311 silver badges21 bronze badges

Comments

Lia · Accepted Answer · 2019-10-08 13:25:22Z

4

The parameters of the super class need to be repeated and passed to the super call:

@Injectable({
    providedIn: 'root'
})
export class UploaderService extends RestService {
  constructor (http: HttpClient){
    super(http);
  }
}

answered Oct 8, 2019 at 13:25

Lia

12k3 gold badges36 silver badges53 bronze badges

3 Comments

Lia Over a year ago

No, It's not a copy. we answered at same time;)

Martin Parenteau Over a year ago

@MostafaSaadatnia - JonasMS's answer was posted before this one. Please check your facts.

Martin Parenteau Over a year ago

@MostafaSaadatnia - For your information, you can see the exact time in a tooltip when the mouse is over "answered ... mins ago". JonasMH answered exactly 12 seconds earlier.

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