Google analytics intercept all requests

Google is actually using gif to sync the data to its server, so intercepting the XHR requests wont work.

In analytics.js there is an official way to do that. via Tasks, here is some small untested example:

ga(function(tracker) {
    var originalSendHitTask = tracker.get('sendHitTask');
    tracker.set('sendHitTask', function(model) {
        var payLoad = model.get('hitPayload');
        originalSendHitTask(model);
        var gifRequest = new XMLHttpRequest();
        var gifPath = "http://localhost/collect";
        gifRequest.open('get', gifPath + '?' + payLoad, true);
        gifRequest.send();
    });
});

make sure that the pageView is sent after this code is executed.

I would demonstrate how you can intercept any AJAX call. Taking from this generic solution, you can filter the GA requests and take the actions you want.

I modified this answer.

The idea behind this solution is modifying the open and send prototype methods of XMLHttpRequest object and do the interception there. The IIFE gets the XMLHttpRequest object, saves the original prototype methods, install new methods and call the original methods from within the new methods. And, of course, do what you want with the data in the mean time.

(function(XHR) {

    //Save the original methods
    var open = XHR.prototype.open;
    var send = XHR.prototype.send;


    //Hook new open method in order to get the url    
    XHR.prototype.open = function(method, url, async, user, pass) {
        this._url = url;

        //Call the original
        open.call(this, method, url, async, user, pass);
    };


    //Hook here too. This will be executed just before the data is sent
    XHR.prototype.send = function(data) {

        if (this_url === GA_URL_CONST)     //Symbolic const  
             SendDataToMyServer(data);     //Symbolic Fn  


        //Call the original
        send.call(this, data);
    }
})(XMLHttpRequest);