title: create Observable<T> from result
body: <p>I am trying Angular2.</p>
  
  <p>I noticed that the http service use <code>Observable</code> object instead of <code>Promise</code> (I don't like much that choice.. <code>async</code>/<code>await</code> are arriving).</p>
  
  <p>In my service, I download a list of <code>Plants</code> from the webservice. Clicking on a plant I show the details using the routing.
  But in this way when I go back, the plants are downloaded again (because the constructor is called again).</p>
  
  <p>To avoid this I want to do something like:</p>
  
  <pre><code>public getPlants(): Observable&lt;Plants[]&gt;
  {   
      if (this._plants != null)
          return Observable.fromResult (this._plants); //This method does not exists 
  
      return this._http.get('../../res/heroes.json')...
  }
  </code></pre>
  
  <p>Is there a way to do that?
  How can I import the <code>Observable</code> class in my ts file?</p>
  
  <p>Thanks!</p>