Show hidden download box after user shares a link
<p>I am trying to make a hidden download box div appear after a visitor shares a link.I've tried here something <a href="http://jsfiddle.net/trefu/qNDJB/4/" rel="nofollow">http://jsfiddle.net/trefu/qNDJB/4/</a> but is not working. I don't know how to define FB so it can be called. Can someone help me?</p>

<pre><code> &lt;div id='fb-root'&gt;&lt;/div&gt;

&lt;div id="download_box" style="display: none;"&gt;
    Download Box (whatever that means) goes here
&lt;/div&gt;

  FB.init({appId: "437410746335629", status: true, cookie: true});

  function postToFeed() {

    // calling the API ...
    var obj = {
      method: 'feed',
      link: 'https://developers.facebook.com/docs/reference/dialogs/',
      picture: 'http://fbrell.com/f8.jpg',
      name: 'Facebook Dialogs',
      caption: 'Reference Documentation',
      description: 'Using Dialogs to interact with users.'
    };

  function callback(response) {
    if (response &amp;&amp; response.post_id) {
        document.getElementById('download_box').style.display = 'block';
    } else {
        alert('You must share your post before you can download.');
    }
}

    FB.ui(obj, callback);
  }
</code></pre>
