Demonstration of cookie availability in XHR callback.

gistfile1.txt

cookie: <div id=cookie> </div>
<? setcookie('c', rand()) ?>
<script type="text/javascript" >
function reqListener () {
console.log(document.cookie);
  document.getElementById('cookie').innerHTML = document.cookie;
}

function fetch() {
  var oReq = new XMLHttpRequest();
  oReq.onload = reqListener;
  oReq.open("get", "", true);
  oReq.send();
}

setInterval(fetch, 1000);
</script>