function getXMLHttpRequest() {
var xhr = null;

if (window.XMLHttpRequest || window.ActiveXObject) {
if (window.ActiveXObject) {
try {
xhr = new ActiveXObject("Msxml2.XMLHTTP");
} catch(e) {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
} else {
xhr = new XMLHttpRequest(); 
}
} else {
alert("Votre navigateur ne supporte pas l'objet XMLHTTPRequest...");
return null;
}

return xhr;
}