// set a global var for the popup window name
var viewer

// opens popup
function openViewer(url) {

closeViewer();

var options = "toolbar=0,scrollbars=auto,resizable=1,width=580,height=600,left=30,top=30";
viewer=window.open(url,"viewerwindow",options);
viewer.focus();
}

// closes window on page unload
function closeViewer(){
	if (viewer && !viewer.closed){
		viewer.close();
	}
}