title: Sort data descending list Firebase Angular2
body: <p>Is it possible to sort values descending using Firebase in Angular2? In my example I want to use the timestamp field as the sort value.</p>
  
  <p>I have tried with this approach but haven't been succesfull in sorting it descending. </p>
  
  <pre><code>this.items = af.database.list('/items', {
        query: {
          orderByChild: 'timestamp'
        }
      });
  </code></pre>
  
  <p>One option I can think of would be pushing these values to a new array as they arrive and then return that array but that seems suboptimal.</p>