AJAX(XMLHTTPRequest)延时

我正在创建一个photogallery页面,并在上面创建了一个Javascript类来管理整个事情。下面是类中调用先前成功初始化的XMLHTTPRequest对象的方法:

this.AJAX_update = function(id) {
    //initialize AJAX - this is done successfully
    this.AJAX_initialize();
    var url = "ScriptLibrary/gallery_update.php?img=" + id;
    //this.ajax_request is an internal variable which is
    //initialized in this.AJAX_initialize() and is
    //XMLHTTPRequest type
    this.ajax_request.open("GET", url, true);
    this.ajax_request.onreadystatechange = processAJAX;
    this.ajax_request.send(null);
}

我不知道如何在onreadystatechange中调用类的内部方法,所以我在类外部创建了一个函数,该函数调用类内部的方法,前提是该类的实例已在其所在的页上创建。页面上类的实例是变量“gallery”。功能如下:

function processAJAX() {
    gallery.AJAX_process();
}

this.AJAX_process = function() {
    if (this.ajax_request.readyState == 4) {
        if (this.ajax_request.status == 200) {
            //get the response
            var response = this.ajax_request.responseXML;

            //Here I set the internal variables according to the value
            //returned from the server
            //...........
            //...........
            //...........

            //change image on the page
            var self = this;
            setTimeout(function() {
                self.swap_dissolve();
            }, 50);

        }
    }
}

所以,我的问题是:

我的代码中任何解决此问题的建议或错误都将非常感谢。

谢谢您。