intercept-network-requests.js

function interceptNetworkRequests(ee) {
    const open = XMLHttpRequest.prototype.open;
    const send = XMLHttpRequest.prototype.send;

    const isRegularXHR = open.toString().indexOf('native code') !== -1;


    // don't hijack if already hijacked - this will mess up with frameworks like Angular with zones
    // we work if we load first there which we can.
    if (isRegularXHR) {
        XMLHttpRequest.prototype.open = function() {
            ee.onOpen && ee.onOpen(this, arguments);
            if (ee.onLoad) {
                this.addEventListener('load', ee.onLoad.bind(ee));
            }
            if (ee.onError) {
                this.addEventListener('error', ee.onError.bind(ee));
            }
            return open.apply(this, arguments);
        };
        XMLHttpRequest.prototype.send = function() {
            ee.onSend && ee.onSend(this, arguments);
            return send.apply(this, arguments);
        };
    }

    const fetch = window.fetch || "";
    // don't hijack twice, if fetch is built with XHR no need to decorate, if already hijacked
    // then this is dangerous and we opt out
    const isFetchNative = fetch.toString().indexOf('native code') !== -1;
    if(isFetchNative) {
        window.fetch = function () {
            ee.onFetch && ee.onFetch(arguments);
            const p = fetch.apply(this, arguments);
            p.then(ee.onFetchResponse, ee.onFetchError);
            return p;
        };
        // at the moment, we don't listen to streams which are likely video 
        const json = Response.prototype.json;
        const text = Response.prototype.text;
        const blob = Response.prototype.blob;
        Response.prototype.json = function () {
            const p = json.apply(this.arguments);
            p.then(ee.onFetchLoad && ee.onFetchLoad.bind(ee, "json"));
            return p;
        };
        Response.prototype.text = function () {
            const p = text.apply(this.arguments);
            p.then(ee.onFetchLoad && ee.onFetchLoad.bind(ee, "text"));
            return p;
        };
        Response.prototype.blob = function () {
            const p = blob.apply(this.arguments);
            p.then(ee.onFetchLoad && ee.onFetchLoad.bind(ee, "blob"));
            return p;
        };
    }
    return ee;
}

interceptNetworkRequests({
    onFetch: console.log,
    onFetchResponse: console.log,
    onFetchLoad: console.log,    
    onOpen: console.log,
    onSend: console.log,
    onError: console.log,
    onLoad: console.log
});