Constructeur Ajax dans classe javascript

function Country()
{
    var ID;
    var Name;
    var Code;

    this.LoadFromXML = function(XMLObject)
    {
        this.ID = (XMLObject.getElementsByTagName("ID_E_COUNTRY")[0].firstChild != null) ? XMLObject.getElementsByTagName("ID_E_COUNTRY")[0].firstChild.nodeValue : "";
        this.Name = (XMLObject.getElementsByTagName("NAME")[0].firstChild != null) ? XMLObject.getElementsByTagName("NAME")[0].firstChild.nodeValue : "";
        this.Code = (XMLObject.getElementsByTagName("CODE")[0].firstChild != null) ? XMLObject.getElementsByTagName("CODE")[0].firstChild.nodeValue : "";

    }

    this.LoadFromXHR = function(SessID, ID)
    {
        var xmlHttp = GetXmlHttpObject(); 
	var URL = "PHP/CountryInfos.php?PHPSESSID=" + SessID;
	var QUERY = "ID=" + ID;
	var METHOD = "POST";
		
	if (xmlHttp == null) 
	{ 
	    alert("Votre navigateur ne supporte pas les requêtes HTTP."); 
	    return false; 
	}			    
	xmlHttp.onreadystatechange = function()
	{ 
	    if (xmlHttp.readyState == 4 || xmlHttp.readyState == "complete")
	    {           	
                  var XmlDoc = xmlHttp.responseXML.documentElement;
		  if(XmlDoc != null)
		  {
			for (i = 0; i < XmlDoc.getElementsByTagName("COUNTRY").length; i++)
			{
				var Objet = XmlDoc.getElementsByTagName("COUNTRY")[i];
				this.LoadFromXML(Objet);
		        }		
	          }        	
	     }
        }
	xmlHttp.open(METHOD, URL, true);
	if(METHOD == 'POST')
	{
		xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;");
	}
	xmlHttp.send(QUERY); 
	return true;
    }
}

this.LoadFromXML(Objet);