var xmlhttp = false;
//------------------------------------------------------------创建XMLHTTP对象----------------------------------------------------------------------//
function CreateXMLHttp() {
    try {
        xmlhttp = new XMLHttpRequest();
    }
    catch (e) {
        try {
            xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e) {
            try {
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (failed) {
                xmlhttp = false;
            }
        }
    }
    return xmlhttp;
}

/**-----------验证用户名是否存在-----------------*/
function validateRegUserIsExist(loginname) {
    xmlHttp = CreateXMLHttp();
    xmlHttp.open("get", "validateUserIsExist.aspx?name=" + loginname + "&rid=" + Math.random(), false);
    xmlHttp.onreadystatechange = function() {
        if (xmlHttp.readyState == 4) {
            if (xmlHttp.status == 200) {
                var jsontext = xmlHttp.responseText;
                flag = jsontext;
            }
        }
    }
    xmlHttp.send();
}