- enhance compatibility to jquery and add responseJSON if datatype is set to JSON - remove references to window, so it can run in a webworker

xhr.js

//Adds $.xhr and jQuery-like $.ajax methods to the prescribed namespace.
//Inspired from David Flanagans excellent cross-platform utils http://www.davidflanagan.com/javascript5/display.php?n=20-1&f=20/01.js
//Includes underscore.js _.each and _.extend methods
//modified to behave like jQuery's $.ajax(), not complete.
(function($) {
    var xhrs = [
           function () { return new XMLHttpRequest(); },
           function () { return new ActiveXObject("Microsoft.XMLHTTP"); },
           function () { return new ActiveXObject("MSXML2.XMLHTTP.3.0"); },
           function () { return new ActiveXObject("MSXML2.XMLHTTP"); }
        ],
        _xhrf = null;
    var hasOwnProperty = Object.prototype.hasOwnProperty,
        nativeForEach = Array.prototype.forEach;
    var _each = function (o, fn, ctx) {
        if (o == null) return;
        if (nativeForEach && o.forEach === nativeForEach)
            o.forEach(fn, ctx);
        else if (o.length === +o.length) {
            for (var i = 0, l = o.length; i < l; i++)
                if (i in o && fn.call(ctx, o[i], i, o) === breaker) return;
        } else {
            for (var key in o)
                if (hasOwnProperty.call(o, key))
                    if (fn.call(ctx, o[key], key, o) === breaker) return;
    }
    };
    var _extend = function (o) {
        _each(Array.prototype.slice.call(arguments, 1), function (a) {
        for (var p in a) if (a[p] !== void 0) o[p] = a[p];
        });
        return o;
    };

    $.xhr = function () {
        if (_xhrf != null) return _xhrf();
        for (var i = 0, l = xhrs.length; i < l; i++) {
            try {
                var f = xhrs[i], req = f();
                if (req != null) {
                    _xhrf = f;
                    return req;
                }
            } catch (e) {
                continue;
            }
        }
        return function () { };
    };
    $._xhrResp = function (xhr) {
        switch (xhr.getResponseHeader("Content-Type").split(";")[0]) {
            case "text/xml":
                return xhr.responseXML;
            case "text/json":
            case "application/json":
            case "text/javascript":
            case "application/javascript":
            case "application/x-javascript":
                return JSON.parse(xhr.responseText);
            default:
                return xhr.responseText;
        }
    };
    $._formData = function (o) {
        var kvps = [], regEx = /%20/g;
        for (var k in o) kvps.push(encodeURIComponent(k).replace(regEx, "+") + "=" + encodeURIComponent(o[k].toString()).replace(regEx, "+"));
        return kvps.join('&');
    };
    $.ajax = function (o) {
        var xhr = $.xhr(), timer, n = 0;
        o = _extend({ userAgent: "XMLHttpRequest", lang: "en", type: "GET", data: null, dataType: "application/x-www-form-urlencoded" }, o);
        if (o.timeout) timer = setTimeout(function () { xhr.abort(); if (o.timeoutFn) o.timeoutFn(o.url); }, o.timeout);
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4) {
                if (timer) clearTimeout(timer);
                if (xhr.status < 300) {
                    
                    if (o.dataType.indexOf("json") >= 0) xhr.responseJSON = JSON.parse(xhr.responseText);

                    if (o.success) o.success($._xhrResp(xhr), "success", xhr);
                }
                else if (o.error) o.error(xhr, xhr.status, xhr.statusText);
                if (o.complete) o.complete(xhr, xhr.statusText);
            }
            else if (o.progress) o.progress(++n);
        };
        var url = o.url, data = null;
        var isPost = o.type == "POST" || o.type == "PUT";
        if (!isPost && o.data) url += "?" + $._formData(o.data);
        xhr.open(o.type, url);

        if (isPost) {
            var isJson = o.dataType.indexOf("json") >= 0;
            data = isJson ? JSON.stringify(o.data) : $._formData(o.data);
            xhr.setRequestHeader("Content-Type", isJson ? "application/json" : "application/x-www-form-urlencoded");
        }
        xhr.send(data);
    };
})(window.yournamespace);