getYouTubePlaylistStats.js

/**
 * Get statistics for YouTube playlists.
 *
 * Navigate to YouTube playlist before executing.
 * For example:
 * https://www.youtube.com/playlist?list=PL3NaIVgSlAVLHty1-NuvPa9V0b0UwbzBd
 */
function getYouTubePlaylistStats() {
    const timeElementsSelector = 'ytd-playlist-video-list-renderer ytd-thumbnail-overlay-time-status-renderer #text';
    const timeElements = Array.from(document.querySelectorAll(timeElementsSelector));
    if (!timeElements.length) throw new Error(`No elements for selector '${timeElementsSelector}'.`);
    const secondsOfEachVideo = timeElements
        .map(element => element.innerText)
        .filter(timeText => timeText)
        .map(timeTextToTimestampArray)
        .map(timestampArrayToSeconds);
    const total = sum(secondsOfEachVideo);
    const count = secondsOfEachVideo.length;
    return {
        count,
        total: secondsToTimestamp(total),
        avg: secondsToTimestamp(total / count),
        min: secondsToTimestamp(Math.min(...secondsOfEachVideo)),
        max: secondsToTimestamp(Math.max(...secondsOfEachVideo)),
    };
}

/**
 * Example Output:
 *    - **Average:** 00:54:17 / 7 = 00:07:45
 *    - **Range:**   00:03:10 - 00:12:27
 */
function format(statistics) {
    const {count, total, avg, min, max} = statistics;
    const indentationLevel = 4;
    const indentation = ' '.repeat(indentationLevel);
    return [
        `**Average:** ${total} / ${count} = ${avg}`,
        `**Range:**   ${min} - ${max}`
    ].map(line => indentation + '- ' + line).join('\n');
}

function sum(array) {
    return array.reduce((sum, value) => sum + value, 0);
}

function secondsToTimestamp(seconds) {
    const date = new Date(0);
    date.setSeconds(seconds);
    return date.toISOString().substring(11, 19);
}

function timestampArrayToSeconds(timestampArray) {
    const [hours, minutes, seconds] = timestampArray;
    return (hours * 60 * 60) + (minutes * 60) + (seconds);
}

/**
 * Example YouTube timeText values: '0:56', '10:08', '9:56:46'.
 */
function timeTextToTimestampArray(timeText) {
    const parts = timeText
        .split(':')
        .map(n => parseInt(n, 10));
    return padArrayLeft(parts, 3, 0);
}

function padArrayLeft(array, length, element) {
    const filledArray = Array(length).fill(element);
    return filledArray.concat(array).slice(array.length); 
}

console.log(format(getYouTubePlaylistStats()));