//重构XMLHttpRequest
var net = new Object();  //名字空間對象

net.READY_STATE_UNINITIALIZED = 0;

net.READY_STATE_LOADING = 1;

net.READY_STATE_LOADED = 2;

net.READY_STATE_INTERACTIVE = 3;

net.READY_STATE_COMPLETE = 4;

net.ContentLoader = function(url, onload, onerror) {   //構造函數

    this.url = url;

    this.req = null;

    this.onload = onload;

    this.onerror = (onerror) ? onerror : this.defaultError;

    this.loadXMLDoc(url);

}

net.ContentLoader.prototype = {

    loadXMLDoc: function(url) {  //重新命名的initXMLHttpRequest函數

        if (window.XMLHttpRequest) {   //重構過的loadXML函數

            this.req = new XMLHttpRequest();

        }

        else if (window.ActiveXObject) {

            this.req = new ActiveXObject("Microsoft.XMLHTTP");

        }

        if (this.req) {

            try {

                var loader = this;

                this.req.onreadystatechange = function() {

                    loader.onReadyState.call(loader);

                }

                this.req.open('GET', url, true); //重構過的sendRequest函數

                this.req.send(null);

            } catch (err) {

                this.onerror.call(this);

            }

        }

    },

    onReadyState: function() {  //重構過的回調函數

        var req = this.req;

        var ready = req.readyState;

        if (ready == net.READY_STATE_COMPLETE) {

            var httpStatus = req.status;

            if (httpStatus == 200 || httpStatus == 0) {

                this.onload.call(this);

            } else {

                this.onerror.call(this);

            }

        }

    },

    defaultError: function() {

        alert("error fetching data!"

        + "\n\nreadyState:" + this.req.readyState

        + "\nstatus:" + this.req.status

        + "\nheaders:" + this.req.getAllResponseHeaders());

    }

}

function myCallBack() {

    alert{this.url

    +" loaded! Here's the content:\n\n"

    +this.req.responseText};

}