Calculates the total duration of a YouTube playlist.

youtube-playlist-duration.js

/*
Calculates the total duration of a YouTube playlist.

Run the snippet in Chrome Dev Tools while on the playlist's page,
e.g. https://www.youtube.com/playlist?list=WL

Ensure that the playlist is fully visible first.
Long playlists are loaded 100 videos at a time.
*/

new Date(1000 *
  [...document.getElementsByTagName('ytd-thumbnail-overlay-time-status-renderer')]
    .map(e => e
      .textContent
      .split(':')
      .reverse()
      .map((n, i) => n * Math.pow(60, i)))
    .flat()
    .reduce((a, b) => a + b, 0))
  .toISOString()
  .substr(11, 8);