get the duration of a youtube playlist

youtube-playlist-duration.js

// scroll down so the entire playlists videos have been fetched, and run this
(() => {
  const sumArray = (arr) => {
    let sum = 0
    for (let seconds of arr) {
      sum+=seconds
    }
    return sum
  }
  const timestampElems = [...document.querySelectorAll('ytd-playlist-video-list-renderer ytd-thumbnail-overlay-time-status-renderer span.style-scope.ytd-thumbnail-overlay-time-status-renderer')]
  const durations = timestampElems.map(e => {
    let parts = e.innerText.split(':')
    let parsed = {}
    if (parts.length===3) {
      parsed.hours = parseInt(parts[0])
      parsed.minutes = parseInt(parts[1])
      parsed.seconds = parseInt(parts[2])
    } else {
      parsed.minutes = parseInt(parts[0])
      parsed.seconds = parseInt(parts[1])
    }
    return ((parsed.hours??0)*60 + parsed.minutes)*60 + parsed.seconds
  })
  let sumInSeconds = sumArray(durations)
  console.log(`${sumInSeconds} seconds, or approximately ${Math.floor(sumInSeconds/(60*60))} hours and ${(Math.ceil(sumInSeconds%(60*60))/60).toFixed(3)} minutes`)
})()