Ajax js scope variabile .........

[whisher]

Ciao.
Stavo cercando di affinare la mia
conoscenza di Ajax su devarticles ho
trovato questo tutorial (leggermente modificato).
La cosa che non mi spiego è lo scope della variabile
data=receiveReq.responseXML.getElementsByTagName(' message');
(Per come la vedo io l'avrei dichiarata all'interno di displayData())
che per quanto ne so dovrebbe essere visibile solo all'interno
della funzione stateChecker() mentre risulta visibile
anche in displayData().
Allego il codice.

<script language="JavaScript" type="text/JavaScript">
function getXmlHttpRequestObject() {
        var receiveReq=false; //Clear our fetching variable
        try {
                receiveReq = new ActiveXObject('Msxml2.XMLHTTP'); //Try the first kind of active x object…
        } catch (e) {
                try {
                        receiveReq = new ActiveXObject('Microsoft.XMLHTTP'); //Try the second kind of active x object
            } catch (e) {
                receiveReq = false;
                        }
        }
        if (!receiveReq && typeof XMLHttpRequest!='undefined') {
               receiveReq = new XMLHttpRequest(); //If we were able to get a working active x object, start an XMLHttpRequest
        }
        return receiveReq;
    }    
    var receiveReq = getXmlHttpRequestObject();        
function getNews( doc ) 
{
    //If our XmlHttpRequest object is not in the middle of a request, start the new asyncronous call.
    if (receiveReq.readyState == 4 || receiveReq.readyState == 0) 
    {
        //Setup the connection as a GET call to your page
        //True explicity sets the request to asyncronous (default).
        receiveReq.open('GET', doc , true);
        //Set the function that will be called when the XmlHttpRequest objects state changes.
        receiveReq.onreadystatechange = stateChecker;
        //Make the actual request.
        receiveReq.send(null);
    }            
}
function stateChecker()
{
    // if request is completed
    if(receiveReq.readyState==4)
    {
        // if status == 200 display text file
        if(receiveReq.status==200)
        {
            // create data container
            createDataContainer();
            // read XML data
          data=receiveReq.responseXML.getElementsByTagName('message'); 

            // display XML data
            displayData();
        }
        else
        {
            alert('Failed to get response :'+ receiveReq.statusText);
        }
    }
}    
function createDataContainer()
{
    var div=document.getElementById('container');
    if(div){return};
    //document.getElementsByTagName('body')[0].removeChild(div);
    var div=document.createElement('div');
    div.setAttribute('id','container');
    document.getElementsByTagName('body')[0].appendChild(div);
}
function displayData()
{
    // reset data container
    document.getElementById('container').innerHTML='';
    var ul=document.createElement('ul');
    for(var i=0;i<data.length;i++)
    {
        // create links
        var li=document.createElement('li');
        var a=document.createElement('a');
        // assign 'href' attribute
        a.setAttribute('href',data[i].getElementsByTagName('url')[0].firstChild.nodeValue);
        // add link labels
        a.appendChild(document.createTextNode(data[i].getElementsByTagName('title')[0].firstChild.nodeValue));
         li.appendChild(a);
         ul.appendChild(li);
    }
    document.getElementById('container').appendChild(ul);
}
window.onload = function()
{
    getNews("news.xml");
}
</script> 

Mi sono perso qc sullo scope delle variabili in JS ?