Ajax Post请求数据中加号变空格的解决方法

//使用post方式发送
function doRequestUsingPOST()
...{
    createXMLHttpRequest();
    var retCode = document.getElementById("retCode").value;
    var data = document.getElementById("data").value;
    data = data.replace(/\\+/g, "%2B");
    data = data.replace(/\\&/g, "%26");
    var queryString = "retCode=" + retCode + "&data=" + data;
    var url = "backSealServlet"; //使用URL向后台传值
    xmlHttp.open("POST",url,false);
    xmlHttp.onreadystatechange = handleStateChange;
    xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xmlHttp.send(queryString);
}