Changing An iframe source from the listbox
<p>I want to change the source of the iframe from a listbox. And here is my code.</p>

<pre><code>&lt;iframe id="iframeID" frameborder="0" width="100%" height="300px"&gt;&lt;/iframe&gt;
   &lt;asp:Button ID="btnView" runat="server" Text="Pop Up HTML Preview" 
               OnClientClick="ShowPopUp();" /&gt;

 ShowPopUp = function() {
      var x = document.getElementById('&lt;%=ListBox1.ClientID %&gt;');
      var val = x.options[x.selectedIndex].Value;
      document.getElementById("iframeID").src = val;
</code></pre>

<p>But error says I have an undefined iframe.<br/>
What is wrong?<br/>
Please help me. Thanks :)</p>
