cvazac

const applyBind = Function.prototype.bind.bind(Function.prototype.apply);
const mapSetApply = applyBind(Map.prototype.set);
const hijackedFns = new Map();
function hijackFunction(context, propName, replacer) {
    mapSetApply(hijackedFns, [replacer, context[propName]]);
    context[propName] = replacer;
}
const fnToStringApply = applyBind(Function.prototype.toString);
const mapGetApply = applyBind(Map.prototype.get);
hijackFunction(Function.prototype, 'toString', function toString() {

cvazac

function wasServedFromBrowserCache(url) {
  const {transferSize, decodedBodySize, duration} = performance.getEntriesByName(url)[0]
  
  // if we transferred bytes, it must not be a cache hit
  // (will return false for 304 Not Modified)
  if (transferSize > 0) return false;

  // if the body size is non-zero, it must mean this is a
  // ResourceTiming2 browser, this was same-origin or TAO,
  // and transferSize was 0, so it was in the cache

cvazac

window.addEventListener('load', function() {
  let totalBytesSaved = 0
  for (const {encodedBodySize, serverTiming} of performance.getEntriesByType('resource')) {
    for (const {name, description} of serverTiming || []) {
      if (name === 'disk') {
        totalBytesSaved += parseInt(description) - encodedBodySize
      }
    }
  }
  console.info('Total Bytes Saved:', totalBytesSaved)

cvazac

(function() {
  let userThinkTime = 0

  ;['alert', 'confirm', 'prompt'].forEach(function(methodName) {
    window[methodName] = (function(method) {
      return function () {
        userThinkTime -= performance.now()
        var returnValue = method.apply(window, arguments)
        userThinkTime += performance.now()
        return returnValue

cvazac

function cachedInBrowser(resourceTimingEntry) {
  if (resourceTimingEntry.requestStart) {
    // has permissive Timing-Allow-Origin response header
    return resourceTimingEntry.transferSize === 0
  }

  // because.... physics?
  return resourceTimingEntry.duration < 30
}

cvazac

!(function() {
    const nativePO = window.PerformanceObserver
    const polyfills = {
      longtask: LongTaskPolyFill
      // etc.
    }
    window.PerformanceObserver = (callback) => {
      let po, registeredPolyFills = []

      const observe = function(options) {

cvazac

!(function() {
    const nativePO = window.PerformanceObserver
    const interfaces = {
      resource: 'PerformanceResourceTiming',
      longtask: 'PerformanceLongTaskTiming',
      // etc.
    }
    const polyfills = {
      longtask: LongTaskPolyFill
      // etc.

cvazac

const query = `
CREATE TEMPORARY FUNCTION getHeaders(payload STRING)
RETURNS STRING
LANGUAGE js AS """
  try {
    var $ = JSON.parse(payload);
    var headers = $.response.headers;
    var st = headers.find(function(e) { 
      return e['name'].toLowerCase() === 'server-timing'
    });

cvazac

(function() {
    if (window !== top) return;

    const bucketSize = 500, threshold = 30, stamps = []
    function measureFps() {
        const now = performance.now()
        if (stamps.length) {
            while (now - stamps[0] > bucketSize) {
                stamps.shift()
            }

cvazac

function isNativeFunction(fn) {
  return typeof fn === 'function' && fn.toString && !fn.hasOwnProperty('toString') &&
      /\[native code\]/.test(String(fn))
}
function checkNatives(fns) {
  var results = []
  for (var i = 0; i < fns.length; i++) {
    results[i] = {
      fn: fns[i],
      native: isNativeFunction(fns[i])