Intercept all ajax calls?

If you're using jQuery, $.ajaxSuccess is a good option, but here's a slightly more generic option that will intercept XHR calls from all frameworks (I've tested it with ExtJS and jQuery - it should work even if multiple frameworks are loaded concurrently). It's been tested to work with IE8, Chrome and Firefox.

(function(XHR) {
    "use strict";

    var open = XHR.prototype.open;
    var send = XHR.prototype.send;

    XHR.prototype.open = function(method, url, async, user, pass) {
        this._url = url;
        open.call(this, method, url, async, user, pass);
    };

    XHR.prototype.send = function(data) {
        var self = this;
        var oldOnReadyStateChange;
        var url = this._url;

        function onReadyStateChange() {
            if(self.readyState == 4 /* complete */) {
                /* This is where you can put code that you want to execute post-complete*/
                /* URL is kept in this._url */
            }

            if(oldOnReadyStateChange) {
                oldOnReadyStateChange();
            }
        }

        /* Set xhr.noIntercept to true to disable the interceptor for a particular call */
        if(!this.noIntercept) {            
            if(this.addEventListener) {
                this.addEventListener("readystatechange", onReadyStateChange, false);
            } else {
                oldOnReadyStateChange = this.onreadystatechange; 
                this.onreadystatechange = onReadyStateChange;
            }
        }

        send.call(this, data);
    }
})(XMLHttpRequest);

I've posted a more specific example on github which intercepts AJAX calls and posts the AJAX call durations back to the server for statistical analysis.

The best way, which I found https://lowrey.me/intercept-2/

const intercept = (urlmatch, callback) => {
  let send = XMLHttpRequest.prototype.send;
  XMLHttpRequest.prototype.send = function() {
    this.addEventListener('readystatechange', function() {
      if (this.responseURL.includes(urlmatch) && this.readyState === 4) {
        callback(this);
      }
    }, false);
    send.apply(this, arguments);
  };
};

From http://api.jquery.com/ajaxSuccess/ :

Whenever an Ajax request completes successfully, jQuery triggers the ajaxSuccess event. Any and all handlers that have been registered with the .ajaxSuccess() method are executed at this time.

So the selector doesn't define the position where you are "catching" the event (because, honestly, ajax event by its nature doesn't start from a DOM element), but rather defines a scope to which the handling will be defaulted (i.e. this will poitn to that/those element(s)).

In summary - it should be exactly what you wish for