实现:以面向对象的形式对ajax请求进行重构

/**
 * 11
 * 原始的 
 */
window.onload = function() {
    document.getElementById("ok").onclick = function() {
        var xmlhttp = ajaxFunction();

        xmlhttp.onreadystatechange = function() {
            if (xmlhttp.readyState == 4) {//响应完毕
                if (xmlhttp.status == 200) {//成功响应
                    alert(xmlhttp.responseText);
                }
            }
        }
        xmlhttp.open("get", "../HelloWorldServlet", true);
        xmlhttp.send(null);
    }

}

// 10
function ajaxFunction() {
    var xmlHttp;
    try { // Firefox, Opera 8.0+, Safari
        xmlHttp = new XMLHttpRequest();
    } catch (e) {
        try { // Internet Explorer
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) {

            }
        }
    }
    return xmlHttp;
}

/**
 * 以面向对象的形式对ajax请求进行重构
 * 
 * 20
 * 
 */
var ajaxObj = {
    // key value
    xmlhttprequest: '',
    getXMLHttpRequest: function() {
        var xmlHttp;
        try { // Firefox, Opera 8.0+, Safari
            xmlHttp = new XMLHttpRequest();
        } catch(e) {
            try { // Internet Explorer
                xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
            } catch(e) {
                try {
                    xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
                } catch(e) {

                }
            }
        }
        return xmlHttp;
    },
    post: function(ajaxJSON) {
        // 给 request 赋值
        ajaxObj.XMLHttpRequest = ajaxObj.getXMLHttpRequest();
        ajaxObj.XMLHttpRequest.onreadystatechange = function() {
            if(ajaxObj.XMLHttpRequest.readyState == 4) {
                if(ajaxObj.XMLHttpRequest.status == 200) {
                    ajaxJSON.callback(xmlhttp.responseText);
                }
            }
        }
        // 
        ajaxObj.XMLHttpRequest.open(ajaxJSON.method, ajaxJSON.url, true);
        ajaxObj.XMLHttpRequest.send(ajaxJSON.data);

    }
}

/**
 * 在onload的时候调用
 * 21
 */
window.onload = function() {
    ajaxObj.post({
        method: 'post',
        url: '../HelloWorldServlet',
        data: 'a=a',
        callback: function(data) {
            alert(data);
        }
    });
}