anchor.diff:  See the https://angular.io/docs/ts/latest/guide/testing.html[Testing chapter] in the Angular 2 Developer Guide for more information on the topic.
   ====
   
  -=== Installing npm packages and starting the development server
  +=== Installing Npm Packages and Starting the Development Server
   
   Install npm dependencies:
   
  
positive.code: ----
  ====
  
  === Npm dependency
  
  Alongside with bower dependencies, we also need to add one npm dependency to the project. `@vaadin/angular2-polymer` package adds support for Polymer elements in Angular 2 component templates. Run this command to install the package and save the dependency in `package.json` at the same time:
  
  
negative.code: ];
  ----
  
  === The Hero Service
  
  We also need a `HeroService` to be able to retrive the heroes list in our Angular application. Add `app/hero.service.ts` file:
  
  