var newWin = null; 
function popUp(strURL, strHeight, strWidth) { 
 if (newWin != null && !newWin.closed) 
   newWin.close();
var strOptions=""; 
   strOptions="status,height="+ 
     strHeight+",width="+strWidth+",top=20,left=20"; 
 newWin = window.open(strURL, 'newWin', strOptions);
 newWin.focus(); 
}