wKoza

export function configFactory(config: ConfigService) {
  return  () => config.load();
}

...


providers: [
    ConfigService,
    {

wKoza

Promise<Article[]> articles = this.http.get('api.learn-angular.fr/articles')
                                      .toPromise()
                                      .then((res: Response) => res.json() as Article[])
                                      .catch(this.handleError);

...

private handleError(error: any): Promise<any> {
    console.error('Une erreur est survenue : ', error); 
    return Promise.reject(error.message || error);

wKoza

import { NgModule }      from '@angular/core';

import { UserService } from './user.service';
import { LogService } from './log.service';

@NgModule({
  imports: [LogService, UserService]
})
class AppModule {
  constructor(logService: LogService, userService: UserService) {

wKoza

import { Component, OnInit } from '@angular/core';
import { LoggerService } from "./logger.service";

@Component({
  selector: 'app-component2',
  template: '<app-component3></app-component3>',
  providers: [LoggerService]
})
export class Component2 implements OnInit {

wKoza

import { Component, OnInit } from '@angular/core';
import { LoggerService } from "./logger.service";

@Component({
  selector: 'app-component1',
  template: '<app-component2></app-component2>',
  providers: [LoggerService]
})
export class Component1 implements OnInit {

wKoza

import { Component, OnInit } from '@angular/core';
import { LoggerService } from "./logger.service";

@Component({
  selector: 'app-component3',
  template: 'Learn Angular !'
})
export class Component3 implements OnInit {

  constructor(private logger:LoggerService) { }

wKoza

import { Component, OnInit } from '@angular/core';
import { LoggerService } from "./logger.service";

@Component({
  selector: 'app-component2',
  template: '<app-component3></app-component3>'
})
export class Component2 implements OnInit {

  constructor(private logger:LoggerService) { }

wKoza

import { Component, OnInit } from '@angular/core';
import { LoggerService } from "./logger.service";

@Component({
  selector: 'app-component1',
  template: '<app-component2></app-component2>',
  providers: [LoggerService]
})
export class Component1 implements OnInit {

wKoza

import {Component} from '@angular/core';
import {LoggerService} from "./logger.service";


@Component({
  selector: 'app-root',
  template: 'Bonjour learn-angular.fr !',
})
export class AppComponent {

wKoza

import { Optional } from '@angular/core';
import { LoggerService } from "./logger.service";

constructor(@Optional() private logger:LoggerService){

    if (this.logger) {
      this.logger.debug('Dans le constructeur ...');
    }
}