// set a global var for the popup window name
var windowName
	
// opens popup
function openviewer(url, width, height) {

	closepop(); 
	
	var options = "toolbar=no,scrollbars=yes,resizable=yes,top=0,left=100,width=" + width + ",height=" + height;
	windowName=window.open(url,"popwindow",options);
	windowName.focus();
}
	
// closes window on page unload
function closeviewer(){
	if (windowName && !windowName.closed){
		windowName.close();
	}
}	
			
// closes window on page unload
function closepop(){
	if (windowName && !windowName.closed){
		windowName.close();
	}
}