Get duplicate requests in JavaScript

deburglar.js

// deburglar.getDupes();
var deburglar = (function () {
    var dict = {};
    var maybeTheOriginalOpen = XMLHttpRequest.prototype.open;
    XMLHttpRequest.prototype.open = function (method, url) {
        if (!dict[url])
            dict[url] = 0;
        dict[url]++;
        return maybeTheOriginalOpen.apply(this, arguments);
    };
    return {
        getDupes: function () {
            return dict;
        }
    };
})();