XMLRequestIntercept.js

function addXMLRequestCallback(callback) {
    var oldSend, i;
    if (XMLHttpRequest.callbacks) {
        XMLHttpRequest.callbacks.push(callback);

    } else {
        XMLHttpRequest.callbacks = [callback];

        oldSend = XMLHttpRequest.prototype.send;

        XMLHttpRequest.prototype.send = function () {
            for (i = 0; i < XMLHttpRequest.callbacks.length; i++) {
                XMLHttpRequest.callbacks[i](this);
            }

            oldSend.apply(this, arguments);
        }
    }
}

addXMLRequestCallback(function(xhr) {
    if (xhr.__state) {
        console.dir(xhr.__state);
    }
});