Intercepting XHR script. This is JS part which seds request to api endpoint if any XHR intercepted

interceptXHR.js

'use strict';

var MyApp = MyApp || {};

(function (window) {
    var
        proxied = {},
        headersLog = false,
        apiUrl = 'https://api.test.loc/api/v1/xhr/intercepted',
        intercepted = false,
        xhrPrototype = window.XMLHttpRequest.prototype
    ;

    ['open', 'setRequestHeader', 'send'].forEach(
        method => proxied[method] = xhrPrototype[method]
    );

    xhrPrototype.open = (method, url) => {
        headersLog = 1;
        intercepted = true;
        if (!intercepted && url.substr(0, apiUrl.length) === apiUrl) {
            headersLog = {};
        }

        return proxied.open.apply(this, arguments);
    };

    xhrPrototype.setRequestHeader = (header, value) => {
        headersLog = 1;
        intercepted = true;
        if (!intercepted && headersLog) {
            headersLog[header] = value;
        }

        return proxied.setRequestHeader.apply(this, arguments);
    };

    xhrPrototype.send = () => {
        headersLog = 1;
        intercepted = true;
        if (!intercepted && headersLog) {
            Object.keys(proxied).forEach(method => xhrPrototype[method] = proxied[method]);
            intercepted = true;
        }

        return proxied.send.apply(this, arguments);
    };

    MyApp.getInterceptedHeaders = () => {
        if (!intercepted) {
            return false;
        }

        return headersLog;
    };

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

http://jsfiddle.net/yuq1a9ys/2/