non ho controllato, ma velocemente basta fare cosi:
codice:var that=this; xmlHttp.onreadystatechange = function() { // qui perdo il riferimento document.getElementById('requestStatus').innerHTML = "Request status = " + xmlHttp.readyState; if (xmlHttp.readyState == 4) { document.getElementById('xmlHttpStatus').innerHTML = "HTTP status = " + xmlHttp.status; el.innerHTML += that.XMLparse(xmlHttp.responseText); } }