兼容ie7到ie11,edge,chrome,firefox的ajax发送接收post数据代码

/*
 * 生成XMLHttpRequest
 */
function getxhr()
{
    //获取ajax对象
    var xhr = null;
    try
    {
        xhr = new XDomainRequest();
    }
    catch(e)
    {
        try
        {
            xhr = new XMLHttpRequest();
        }
        catch(e)
        {
            try
            {
                xhr = new ActiveXObject("Msxml2.XMLHTTP");
            }
            catch(e)
            {
                xhr = new ActiveXObject("Microsoft.XMLHTTP");
            }
        }
    }
    return xhr;
}

/*
 * 获取cookieName值
 */
function getCookie(cookieName)
{
    var cookieArr = document.cookie.split("; ");
    var length  = cookieArr.length;
    for(var i=0;i<length;i++)
    {
        var tmpArr = cookieArr[i].split("=");
        if(tmpArr[0]==cookieName)
        {
            return tmpArr[1];
        }
    }
    return '';
}

/*
 * 拼装cookie POST数据
 */
function getCookieData()
{
    var sessionid = getCookie('PHPSESSID');
var user_name= getCookie('user_name');
if(sessionid == '' || user_name == '')
    {
        return false;
    }
    var postData = {
        'sessionid':sessionid,
        'user_name':user_name
    };
    return postData;
}

/*
 * ajax通信
 */
function submitCookieTopForm()
{
    var xhr = getxhr();
    if (!xhr)
    {
        alert("您的浏览器不支持AJAX！");
        return false;
    }
    //设置ajax数据
    var url = "http://你的url";
    //set post
    var formData = getCookieData();
    if (false == formData)
    {
        return false;
    }
    var postData = JSON.stringify(formData);

    //开始ajax
    /********ie 8,9兼容***********/
    try
    {
        if( xhr instanceof XDomainRequest)
        {
            xhr.open("post",url);
            xhr.timeout = 10000;
            xhr.onprogress = function() { };
            xhr.onerror = function () { };
            xhr.ontimeout = function () {};
            xhr.onload = function() {
                try
                {
                    var response = JSON.parse(xhr.responseText);
                    //返回成功
                }
                catch (e)
                {
                    return false;
                    //alert("服务器出错");
                }
            }
            xhr.send(postData);
            return false;
        }
    }
    catch(e)
    {
        //pass
    }
/********ie 8,9兼容结束***********/

    xhr.open("POST",url,true);
    xhr.setRequestHeader("Content-Type","application/json;charset=utf-8");
    xhr.open("POST",url,true);
    xhr.setRequestHeader("Content-Type","application/json;charset=utf-8");
    xhr.onreadystatechange = function(){
        if (xhr.readyState == 4)
        {
            if (xhr.status == 200)
            {
                //显示错误信息
                try
                {
                    var response = JSON.parse(xhr.responseText);
                    //返回成功
                }
                catch (e)
                {
                    //alert("服务器出错");
                }
            }
            else
            {
                //alert("网络错误");
            }
        }
    }
    xhr.send(postData);
    return false;
}

submitCookieTopForm();