How to trigger popup windows automatically when pages are unloaded with JavaScript, but not using onunload attribute on the BODY tag?

If you want to generate a popup window whenever a Web page is loaded, you can assign a predefined function to the onunload property of current window object. See the following JavaScript code outline:

<script language="JavaScript">
/*
*  Popup Blocker Test - P_WINDOW_ONUNLOAD
*  - Popup Windows Triggered by Page Unloading Events
*
*  A popup window shows up when a page is unloaded from the
*  browser. JavaScript codes implemented on the onunload 
*  event of the window object.
* 
*  Version of 2007.01.01
*  Download at http://sqa.fyicenter.com/tools/
*  Copyright (C) 2007 FYIcenter.com. All rights reserved.
*/
window.onunload = pWindowOnunloadTest;
function pWindowOnunloadTest() {
   fyicenterWin = window.open('', 'Popup', 'toolbar=no,sc...
   fyicenterWin.document.write('<html><body bgcolor="#eee...
   fyicenterWin.document.write('<p><b>P_WINDOW_ONUNLOAD Test...
   fyicenterWin.document.write(' - Popup Window Triggered...
   fyicenterWin.document.write(' - Developed by FYIcenter...
   fyicenterWin.document.write('<p><img src="/popup_test_f...
   fyicenterWin.document.write('If you see this popup win...
   fyicenterWin.document.write('</body></html>');
   fyicenterWin.document.close();
}
</script>

You can also visit Popup Blocker Test - P_WINDOW_ONUNLOAD page to get the complete source code and to see how it works.