Angular2 DI

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { RouterModule } from '@angular/router';

import { AppComponent } from './app.component';

import { CoreModule } from './core/core.module';

@NgModule({
  imports: [
    BrowserModule,
    CoreModule,
    RouterModule.forRoot([])
  ],
  declarations: [ AppComponent ],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';

import { AppModule } from './app.module';

platformBrowserDynamic().bootstrapModule(AppModule);

<!DOCTYPE html>
<html>
  <head>
    <title></title>
    <base href="." />
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="styles.css">

    <!-- Polyfills for older browsers -->
    <script src="https://unpkg.com/core-js/client/shim.min.js"></script>

    <script src="https://unpkg.com/zone.js@0.7.4?main=browser"></script>
    <script src="https://unpkg.com/reflect-metadata@0.1.8"></script>
    <script src="https://unpkg.com/systemjs@0.19.39/dist/system.src.js"></script>

    <script src="https://cdn.rawgit.com/angular/angular.io/b3c65a9/public/docs/_examples/_boilerplate/systemjs.config.web.js"></script>
    <script>
      System.import('app').catch(function(err){ console.error(err); });
    </script>
  </head>

  <body>
    <app>Loading...</app>
  </body>

</html>


<!-- 
Copyright 2016 Google Inc. All Rights Reserved.
Use of this source code is governed by an MIT-style license that
can be found in the LICENSE file at http://angular.io/license
-->

import { NgModule, Optional, SkipSelf } from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpModule } from '@angular/http';

import { throwIfAlreadyLoaded } from './module-import-guard';
import { AuthService } from './auth.service';
import { ConsoleLogger } from './console-logger';
import { ErrorHandler } from './error-handler';

@NgModule({
  imports: [
    CommonModule,
    HttpModule,
  ],
  providers: [
    AuthService,
    ConsoleLogger,
    ErrorHandler,
  ],
})
export class CoreModule {
  constructor(@Optional() @SkipSelf() parentModule: CoreModule) {
    throwIfAlreadyLoaded(parentModule, 'CoreModule');
  }
}

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

@Injectable()
export class ConsoleLogger {
  debug(message: string): void {
    console.debug(message);
  }

  error(message: string): void {
    console.error(message);
  }

  info(message: string): void {
    console.info(message);
  }

  warn(message: string): void {
    console.warn(message);
  }
}

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';

import { ConsoleLogger } from './console-logger';
import { Credentials } from './credentials';
import { ErrorHandler } from './error-handler';

@Injectable()
export class AuthService {
  constructor(
     private logger: ConsoleLogger,
     private errorHandler: ErrorHandler,
     private http: Http) {}

  login(credentials: Credentials): Observable<any> {
    this.logger.info('Foo!');
    const url = 'https://mywebsite.com/api';
        
    return this.http.post(url, JSON.stringify(credentials))
                    .map((response: Response) => {
                        // store access token
                    })
                    .catch(this.errorHandler.handleError);
    }
}

import { Injectable } from '@angular/core';
import { Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { ErrorObservable } from 'rxjs/Observable/ErrorObservable';

import { ConsoleLogger } from './console-logger';

@Injectable()
export class ErrorHandler {
  constructor(private logger: ConsoleLogger) {
    logger.debug('ErrorHandler inizialized');
  }

  handleError(response: Response | any): ErrorObservable<string> {
    let errorMessage: string = 'Bar!';
    this.logger.error(errorMessage);
        
    return Observable.throw(errorMessage);
  }
}

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

import { AuthService } from './core/auth.service';
import { Credentials } from './core/credentials';

@Component({
  selector: 'app',
  template: `
    <button (click)=login()>Login</button>
  `,
})
export class AppComponent {
  constructor(private authService: AuthService) {}
  
  login() {
    const credentials: Credentials = {
      email: 'foo',
      password: 'bar'
    }
    this.authService.login(credentials).subscribe();
  }
}

export class Credentials {
  public email: string;
  public password: string;
}

export function throwIfAlreadyLoaded(parentModule: any, moduleName: string): void {
  if (parentModule) {
    throw new Error(`${moduleName} has already been loaded. Import Core modules in the AppModule only.`);
  }
}