var xmlhttp = false;
//Check if IE
try {
        xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e) {
        try {
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
        catch (E) {
                xmlhttp = false;
        }
}

if(!xmlhttp && typeof XMLHttpRequest != 'undefined') {
        xmlhttp = new XMLHttpRequest();
}