ajax

var req;

function autorequest(){
url = "client/xml_client_req.php?auto=" + document.getElementById("support_id_field").innerHTML;
if (window.XMLHttpRequest){//non-IE
req = new XMLHttpRequest();
req.onreadystatechange = autorequestStateChange;
try{
req.open("GET", url, true);
}catch (e){
alert (e);
}
req.send(null);
}else if(window.ActiveXObject){//IE
req = new ActiveXObject("Microsoft.XMLHTTP");
if(req){
req.onreadystatechange = autorequestStateChange;
req.open("GET", url, true);
req.send();
}
}
}
function autorequestStateChange(){
if(req.readyState == 4){
if(req.status == 200){
xml = req.responseXML;
html = '';
i = 0;
while (i >= 0){
sto = xml.getElementsByTagName("sto")[i];
wms = xml.getElementsByTagName("wms")[i];
msg = xml.getElementsByTagName("msg")[i];
if(sto != null){
sto = sto.firstChild.data;
}
if(wms != null && msg != null){
wms = wms.firstChild.data;
msg = msg.firstChild.data;
if (msg == 'c'){
sender = '>';
color = '#FFFFFF';
}
if (msg == 'm'){
sender = '>>';
color = '#FF0000';
}
html += '<div style="color:' + color + '">' + sender + ' ' + msg + '</div>';
i++;
}else{
i = -1;
}
}
i = 0;
document.getElementById("status_top").innerHTML=sto;
document.getElementById("chat_ontvangen").innerHTML=html;
}else{
alert("Problem: " + req.statusText);
}
}
}

xml:

<auto>
<sto>Mathias</sto>
<wms>c</wms>
<msg>testje</msg>
<wms>o</wms>
<msg>testje</msg>
</auto>

js debugger geeft dit:
[e] message = [string] "sto.firstChild has no properties"