ajax重构XMLHttpRequest

//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};
}