YouTube ページ ナビゲーションをシームレスに検出して変更するにはどうすればよいですか?

{
  "matches": ["*://*.youtube.com/*"],
  "js": ["content.js"],
  "run_at": "document_start"
}

document.addEventListener('yt-navigate-start', process);
if (document.body) process();
else document.addEventListener('DOMContentLoaded', process);

function process() {
  if (!location.pathname.startsWith('/playlist')) return;
  var seconds = [...document.getElementsByClassName('timestamp')]
    .reduce((sum, ts) => {
      const minsec = ts.textContent.split(':');
      return sum + minsec[0] * 60 + minsec[1] * 1;
    }, 0);

  if (!seconds) {
    console.warn('Empty playlist');
    return;
  }

  const timeHMS = new Date(seconds * 1000)
    .toUTCString()
    .split(' ')[4]
    .replace(/^[0:]+/, '');

  document
    .querySelector('.pl-header-details')
    .insertAdjacentHTML('beforeend', `<li>Length: ${timeHMS}</li>`);
}