Jawa script Синтаксис

Как сюда вставить значения функции response?

Code:

function file_get_contents_async( url ,callback) {
var req = null;
   try { req = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) {
      try { req = new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) {
         try { req = new XMLHttpRequest(); } catch(e) {}
      }
   }
   if (req == null) throw new Error('XMLHttpRequest not supported');

req.open("GET",url,true);
req.onreadystatechange=function() {
  if (req.readyState==4) {
   var response = req.responseText;
   callback(response);
 }};
req.send(null);
}


file_get_contents_async('http://api.vkontakte.ru/method/users.get?uids=1&fields=photo_200',function(response) {
   //response is the downloaded string...
   //BE WARNED THAT : if download fails no call is made
   alert(response);
var obj = ([B][COLOR=Red]Как сюда вставить значения функции response?[/COLOR][/B]);
var uid = obj.response[0].uid;
var firstName = obj.response[0].first_name;
var lastName = obj.response[0].last_name;
var avatar = obj.response[0].photo_200;
alert(lastName);
 });

 

https://github.com/douglascrockford/JSON-js