title: How to detect if a browser window is closed?
body: <p>How can I detect if a browser window was closed?
  I am opening a web page from my site in a new browser window.</p>
  
  <p>I know people generally use <code>unload</code> event but the browser window that I am opening is a page which is not a part of my web site(e.g. www.google.com).</p>
  
  <p>Is there any way to detect this?</p>