ajax 通用方法

var xmlHttp;
// 创建XMLHttpRequest对象
function createXMLHttpRequest() {
    try {
        // FireFox, Opera 8.0 +, Safari
        xmlHttp = new XMLHttpRequest();
    }
    catch (e) {
        try {
            // IE 6.0 +
            xmlHttp = new ActiveXObject('MSXML2.XMLHTTP');
        }
        catch (e) {
            try {
                // IE 5.5 +
                xmlHttp = new ActiveXObject('Microsoft.XMLHTTP');
            }
            catch (e) {
                alert('您的浏览器不支持AJAX！');
                return false;
            }
        }
    }
}
function SendContent(url, type, data, handleMethod) {
    createXMLHttpRequest();
    xmlHttp.open(type, url);
    xmlHttp.onreadystatechange = function() { postBack(handleMethod); };
    xmlHttp.send(data);
}
function postBack(method) {
    if (xmlHttp.readyState == 4) {
        if (xmlHttp.status == 200) {
            //var r