Navigation Timing https://www.w3.org/TR/navigation-timing/#sec-window.performance-attribute

main.js

window.addEventListener('load', () => {
  const t = performance.timing
  // Log performance details:
  for (const key of [
    'fetchStart',
    'connectStart',
    'connectEnd',
    'requestStart',
    'responseStart',
    'responseEnd',
    'domComplete'
  ])
  console.log(key, t[key] - t.navigationStart + 'ms')
})

// fetchStart 1ms
// connectStart 10ms
// connectEnd 10ms
// requestStart 10ms
// responseStart 59ms
// responseEnd 75ms
// domComplete 762ms