function getXmlHttpObject() {
    if (window.XMLHttpRequest) {
        // code for IE7+, Firefox, Chrome, Opera, Safari
        return new XMLHttpRequest();
    }
    if (window.ActiveXObject) {
        // code for IE6, IE5
        return new ActiveXObject("Microsoft.XMLHTTP");
    }
    return null;
}

function getAjaxResponse(url, paras, idx) {
    var xmlhttp = getXmlHttpObject();
    xmlhttp.onreadystatechange=function () {
        if (xmlhttp.readyState == 4) {
            if (xmlhttp.status == 200) {
                processAjaxResponse(xmlhttp.responseText, idx);
            } else {
                alert("Problem retrieving XML data:" + xmlhttp.statusText);
            }
        }    
    };
    xmlhttp.open("post", url, true);
    xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    xmlhttp.send(paras);    
}