title: angular tutorial could not receive data from http call
body: <p>I am trying to learn Angular 2 by following the Tutorial Step 7 HTTP (<a href="https://angular.io/tutorial/toh-pt6" rel="nofollow noreferrer">https://angular.io/tutorial/toh-pt6</a>). However the function <code>getHeroes()</code> in <code>hero.service.ts</code> still return nothing.</p>
  
  <pre><code>getHeroes(): Promise&lt;Hero[]&gt; {
      return this.http.get(this.heroesUrl)
      .toPromise()
      .then(response =&gt; response.json().data as Hero[])
      .catch(this.handleError);
  } 
  </code></pre>
  
  <p>where the mock service is implemented from <code>InMemoryDbService</code>.</p>
  
  <p>Any idea please?</p>