Mini AJAX Library

// constructor function with name of class. JScript does not really have classes and neither is this like a
//PHP constructor class http://php.net/manual/en/language.oop5.decon.php
function Ajax() {
    // properties which are variables or constants in PHP5
    this.req = null;
    this.url = null;
    this.method = 'GET';
    this.asynch = true;
    this.status = null;
    this.statusText = '';
    this.postData = null;
    this.readyState = null;
    this.responseText = null;
    this.responseXML = null;
    this.handleResp = null;
    this.responseFormat = 'text',
    // 'text', 'html', 'xml' or 'object'
    this.mimeType = null;

}
// End Constructor
//Create XMLHttpRequest method with  XMLHttpRequest object
//Ajax.prototype.init
//this.init = function() {
    Ajax.prototype.init = function () {
    if (!this.req) {
        try {
            //Try to create objects for Firefox, Safari, IE7, etc.
            this.req = new XMLHttpRequest();
        }

        catch(e) {
            try {
                //Try to create object for later versions of IE.
                this.req = new ActiveXObject('MSXML2.XMLHTTP');
            }

            catch(e) {
                try {
                    //Try to create for early versions of IE.
                    this.req = new ActiveXObject('Microsoft.XMLHTTP');
                }

                catch(e) {
                    //Could not create XMLHttpRequest object.
                    return false;
                }
            }
        }
    }
    return this.req;
};


//Sending a Request method
Ajax.prototype.doReq = function() {
    if (!Ajax.prototype.init()) {
        alert('Could not create XMLHttpRequest object.');
        return;
    }
    //Setting up a request
    //open methods with method, url and asycn yes or no
    Ajax.prototype.req.open(this.method, this.url, this.asynch);
    //Make sure mimetype is OK
    if (this.mimeType) {
        try {
            req.overrideMimeType(this.mimeType);
        }
        catch(e) {
            //couldn't override MIME type ... IE6 or Opera?
            }
    }

    //var self = this;
    // fix loss-of-scope in inner function
    Ajax.prototype.req.onreadystatechange = function() {
        var resp = null;
        if (Ajax.prototype.req.readyState == 4) {
            //do stuff to handle response
            switch (this.reponseFormat) {
            case 'text':
                resp = this.req.responseText;
                break;
            case 'xml':
                resp = this.req.responseXML;
                break;
            case 'object':
                resp = req;
                break;
            }
            if (Ajax.prototype.status >= 200 && Ajax.prototype.req.status <= 299) {
                this.handleResp(resp);
            }
            else {
                Ajax.prototype.handleErr(resp);
            }
        }

    };
    Ajax.prototype.req.send(this.postData);
};

Ajax.prototype.handleErr = function() {
    var errorWin;
    try {
        errorWin = window.open('', 'errorWin');
        errorWin.document.body.innerHTML = this.responseText;
    }
    catch(e) {
        alert('An error occured, but this error message cannot be '
        + 'displayed. This is probably because of your browser\'s '
        + 'pop-up blocker. \n'
        + 'Please  allow pop-ups from this website if you want to '
        + 'see the full error messages. \n'
        + '\n'
        + 'Status Code: ' + this.req.status + '\n'
        + 'Status description: ' + this.req.statusText);
    }
};

Ajax.prototype.abort = function() {
    if (this.req) {
        this.req.onreadystatechange = function() {};
        this.req.abort();
        this.req = null;
    }
};

Ajax.prototype.doGet = function (url, hand, format) {
    this.url = url;
    this.handleResp = hand;
    this.responseFormat = format || 'text';
    this.doReq();
};