var winopener=null;

function popupwindow(choice,wt,ht)
{ 

if(winopener){
 winopener.close();
}

var winOpts="toolbars=no,maximize=no,resize=no,width="+wt+",height="+ht+",location=no,directories=no";
winopener=window.open(choice,'pattern',winOpts);
winopener.focus();

}