title: angular2 map data as specific object type
body: <p>I created a very simple app based on the Angular2 tutorial. </p>
  
  <p>To start, I have a very simple "Book" model:</p>
  
  <pre><code> /**
   * book model
   */
  export class Book {
      public data;
  
      /**
       * constructor
       * @param id
       * @param title
       * @param pages
       */
      constructor(
          public id,
          public title:string,
          public pages:Array
      ){
          alert('it works'); // just a check
      }
  }
  </code></pre>
  
  <p>In my service, I get a book like this:</p>
  
  <pre><code>return this._http.get('getBook/1')
          .map(function(res){
              return &lt;Book&gt; res.json();
          })
  </code></pre>
  
  <p>My expectation was that this would get the resulting JSON data and "map" it to a Book object.</p>
  
  <p>However, it just returns an object with type "Object".</p>
  
  <p>I could create a new Book object myself and pass the parameters in the constructor, like this:</p>
  
  <pre><code>return new Book(res.id, res.title, res.pages);
  </code></pre>
  
  <p>Is this the best way to do this? Did I miss something?</p>