I'm developing a simple auxiliary class to send requests using XmlHttpRequest (code below). But I cant make it work. At google chrome, for example, I get the error INVALID_STATE_ERR: DOM Exception 11 and at the other browsers I get a status == 0.

//@method XRequest: Object constructor. As this implements a singleton, the object can't be created calling the constructor, GetInstance should be called instead

function XRequest() {

    this.XHR = XRequest.CreateXHR();

}

XRequest.instance = null;



//@method static GetInstance: Creates a singleton object of type XRequest. Should be called whenever an object of that type is required.

//@return: an instance of a XRequest object

XRequest.GetInstance = function() {

    if(XRequest.instance == null) {

        XRequest.instance = new XRequest();

    }

    return XRequest.instance;

}



//@method static CreateXHR: Implments a basic factory method for creating a XMLHttpRequest object

//@return: XMLHttp object or null

XRequest.CreateXHR = function() {

    var xhr = null;

    var factory = [

        function() { return new XMLHttpRequest(); },

        function() { return new ActiveXObject(Msxml2.XMLHTTP); },

        function() { return new ActiveXObject(Microsoft.XMLHTTP); }

    ];



    for(var i = 0; i < factory.length; ++i) {

        var f = factory[i];

        xhr = f();

        if(xhr) return xhr;

    }

    return null;

}



XRequest.prototype.SetRequestHeader = function(name, value) {

    if(this.XHR) {

        this.XHR.setRequestHeader(name, value);

    }

}



XRequest.prototype.SendRequest = function(args) {

    var async = true;

    var type = ;

    var url = ;

    var username = ;

    var password = ;

    var body = null;

    var success = null; 

    var failure = null;



    for(e in args) {

        switch(e) {

            case async:

                async = args[e];

                break;

            case type:

                type = args[e];

                break;

            case success:

                success = args[e];

                break;

            case failure:

                failure = args[e];

                break;

            case url:

                url = args[e];

                break;

            case username:

                username = args[e];

                break;

            case password:

                password = args[e];

                break;

            case body:

                body = args[e];

            break;

            case setHeader:

                var h = args[e].split(:);

                if(h.length == 2) {

                    this.SetRequestHeader(h[0], h[1]);

                }

                break;

        }

    }



    var that = this;

    this.XHR.onreadystatechange = function() {

        alert(readyState ==  + that.XHR.readyState +   status ==  + that.XHR.status);

        if(that.XHR.readyState == 4) {

            if(that.XHR.status == 200 || that.XHR.status == 0) {

                if(success) success(that.XHR);

            } else {

                if(failure) failure();

            }

        }

    };

    this.XHR.open(type, url, async, username, password);

    this.XHR.send(body);

}

Example of usage:

<script language=javascript>

    function onLoad() {

        var x = XRequest.GetInstance();

        x.SendRequest({type:GET,

            setHeader:Accept:text/html, image/png, image/*, */*,

            url: http://your_server.com/getData?param1=test,

            success:onSuccess, failure:onFail

        });

    }



    function onSuccess(obj) {

        alert(OK);                

    }



    function onFail() {

        alert(Not at this time!);

    }

</script>