servicesingelton5.js

import { Injectable } from '@angular/core';
import { RootInjectorGuard } from './root-injector.guard';

@Injectable({
  providedIn: 'root'
})
export class AppService extends RootInjectorGuard  {

  constructor() { 
    super(AppService)
  }

  getData(){
    return "data";
  }
}