国内首发 -- ajax完整功能框架

        xmldoc = false;
    //Mozill,Safari等浏览器时需要创建的XMLHttp类
        if(window.XMLHttpRequest){
            xmldoc = new XMLHttpRequest();
            if(xmldoc.overrideMimeType){
                    xmldoc.overrideMimeType('text/xml');
            }
        }
    //IE浏览器时创建的XMLHttp类
        else if(window.ActiveXObject){
            try{
                xmldoc = new ActiveXObject("Msxml3.XMLHTTP");
            }
            catch(e){
                try{
                    xmldoc = new ActiveXObject("Msxml2.XMLHTTP");
                }
                catch(e){
                    try{
                        xmldoc = new ActiveXObject("Microsoft.XMLHTTP");
                    }
                    catch(e){}
                }
            }
        }
    //不能创建XMLHTTP类时返回
        if(! xmldoc){
            return false;
        }
    //调用CheckState函数
        xmldoc.onreadystatechange = CheckState;
        xmldoc.open('GET',url,true);
        xmldoc.send(null);