Script to intercept XMLHttpRequest calls made by some page.

Tampermonkey-XHR-Intercept.js

/* Intercept XMLHttpRequests */

(function(open) {
    XMLHttpRequest.prototype.open = function() {
        this.addEventListener("readystatechange", function() {
            console.log("readyState: "+this.readyState);
        }, false);
        open.apply(this, arguments);
    };
})(XMLHttpRequest.prototype.open);