Centered popup window

function popUp(theURL, myWidth, myHeight) {
var winName = 'feedback';
var features='toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=0';
//var myWidth = 290;
//var myHeight = 360;
var isCenter = 'true';
 if(window.screen)if(isCenter)if(isCenter=="true"){
   var myLeft = (screen.width-myWidth)/2;
   var myTop = (screen.height-myHeight)/2;
   features+=(features!='')?',':'';
   features+=',left='+myLeft+',top='+myTop;
 }
 var handle = window.open(theURL,winName,features+((features!='')?',':'')+'width='+myWidth+',height='+myHeight);
  handle.opener = window;
  handle.focus();
 return handle;
}