ajax起步

写了个ajax调用的js，以备自己以后再用

js 代码

var xmlHttp;
function createXMLHttpRequest(){
    if (window.ActiveXObject){
        var version = ["MSXML2.XMLHttp.5.0","MSXML2.XMLHttp.4.0",
                       "MSXML.XMLHttp.3.0","MSXML.XMLHttp","Microsoft.XMLHttp"];
        for(var i = 0; i < version.length; i++ ){
            try{
                var oXmlHttp =  new ActiveXObject(version[i]);
                return oXmlHttp;
            }catch(oError){}
        }
    }else if (window.XMLHttpRequest){
        var oXmlHttp = new XMLhttpRequest();
        return oXmlHttp;
    }
    throw new Error("不能创建XMLHttp对象，请确认您的电脑上已安装了XMLHttp对象!");
}
function sendRequest(url,param,callBack,sync) {
    if(!xmlHttp) xmlHttp = createXMLHttpRequest();
    xmlHttp.open("post",url,sync);
    xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
    xmlHttp.onreadystatechange = function() {
        if (xmlHttp.readyState == 4) {
            if (xmlHttp.status == 200) {
                 callBack(xmlHttp.responseXML);
            }
        }
    }
    xmlHttp.send(param);
}
function addParam(params,paramName,paramValue) {
   var param = encodeURIComponent(paramName) + "=" + encodeURIComponent(paramValue);
   params.push(param);
}
function getParams(params) {
   var time = new Date().getTime();
   params.push(time);
   return params.join("&");
}