quit-inside-unload.html

   1 <script>
   2     var showedAlert = false;
   3     function handleUnload()
   4     {
   5         if (showedAlert)
   6             return;
   7
   8         showedAlert = true;
   9         alert("Now Quit Safari. Do not dismiss this alert first.");
  10     }
  11 </script>
  12 <body onunload="handleUnload()">
  13     Close this window
  14 </body>