function Xhr() // http://fr.wikipedia.org/wiki/XMLHttpRequest
{
    if (window.XMLHttpRequest)
        return new XMLHttpRequest();
 
    if (window.ActiveXObject)
    {
        var names = [
            "Msxml2.XMLHTTP.6.0",
            "Msxml2.XMLHTTP.3.0",
            "Msxml2.XMLHTTP",
            "Microsoft.XMLHTTP"
        ];
        for(var i in names)
        {
            try{return new ActiveXObject(names[i]);}
            catch(e){}
        }
    }
    window.alert("Error !");
    return null;
}