function getTimeToInteractive() {
  const domInteractive = window.performance.timing.domInteractive;
  const requestStart = window.performance.timing.requestStart;
  
  return domInteractive - requestStart;
}
/*
 * returns: [
 * {
 *    name: 'haha.js',
 *    duration: 12313,
 *    transferSize: [bytes || 0 if served from cache]
 * }]
*/
function getResourceEntries() {
  return window.performance.getEntriesByType('resource') || []; 
}

/*
 * Browser support: full
 * Success rate: > 95%
 * Can prefetch HTML: no
 */
function prefetchResource(resourceURL) {
  const xhrRequest = new XMLHttpRequest();
  xhrRequest.open('GET', resourceURL, true);
  xhrRequest.send();
}