INVALID_STATE_ERR: DOM Exception 11

Question

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 INVALI

Answer 1

Problem in this ajax library.

XHR.setRequestHeader() must be called after XHR.open().

// @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)
    {
        //alert(name+'|||'+value);
        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;
        }
    }

    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);
    for(e in args)
    {
        switch(e)
        {
            case "setHeader":
                var h = args[e].split(":");             
                if(h.length == 2)
                {
                    this.SetRequestHeader(h[0], h[1]);
                }
                break;
        }
    }
    this.XHR.send(body);
}