title: ASP.NET: Warning on changed data closing windows
body: <p>I'd like to warn users when they <strong>try to close a browser window</strong> if they <strong>didn't save</strong> the changes they made in the web form.</p>
  
  <p>I'm using ASP.NET 3.5 (with ASP.NET Ajax).</p>
  
  <p>Is there a common solution which I could easily implement?</p>
  
  <p><em>EDIT: maybe my question wasn't clear:</em> I am specifically looking for a way which integrates gracefully in the <strong>ASP.NET</strong> Server Controls methodology.</p>