XHR and JSON is all you really need

xhr.js

(function(context) {
    var xhr = context.XMLHttpRequest,
        json = context.JSON,
        mime = 'application/json';

    context.xhr = xhr && json && function(method, url, data, callback) {
        var req = new xhr();

        req.onreadystatechange = function() {
            if(req.readyState == 4) {
                var status = req.status,
                    body,
                    err;

                try {
                    if (status > 0) {
                        body = req.responseText;
                        body = body ? json.parse(body) : err;
                    } else {
                        err = req;
                    }
                }
                catch (e) {
                    err = e;
                }

                if (callback) {
                    callback(err, status, body);
                    callback = null;
                }
                req.onreadystatechange = null;
            }
        };

        req.open(method, url, true);
        req.setRequestHeader('Accept', mime);
        req.setRequestHeader('Content-Type', mime);
        //req.withCredentials = true;
        req.send(data ? json.stringify(data) : null);
    };
}(this));