title: validate either both textbox should be filled or both should be empty
body: <p>I've two textboxes. I need to validate whether both the textboxes are filled, only one textbox can not be filled. </p>
  
  <pre><code>&lt;asp:TextBox ID="testTxtName" runat="server" /&gt;
  &lt;asp:TextBox ID="testTxtGroup" runat="server" /&gt;
  </code></pre>
  
  <p>I need to do this validation on submit button click.
  So the user has to fill both the textboxes or both should be left empty. Filling only one textbox is error. How can I do this using javascript?</p>