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YouTube Time Remaining

Display the remaining time of a YouTube video during playback.

As of 2021-07-01. See the latest version.

// ==UserScript==
// @name            YouTube Time Remaining
// @description     Display the remaining time of a YouTube video during playback.
// @version         1.7.2
// @author          stinkrock
// @license         MIT
// @namespace       patchmonkey
// @match           https://www.youtube.com/*
// @run-at          document-idle
// @noframes
// ==/UserScript==


const STREAM = '.video-stream.html5-main-video'

const CONTAINER = 'ytd-video-primary-info-renderer #container #info'

const PLAYER = 'yt-player-updated'

const PAGE = 'yt-page-data-updated'


const create = x => document.createElement(x)

const text = x => document.createTextNode(x)

const append = (x, y) => x.appendChild(y)

const query = x => y => y.querySelector(x)


const comp = (f, g) => x => g(f(x))

const compose = (...f) => f.reduce(comp)


const each = x => f => f(x)

const list = (...f) => x => f.map(each(x))

const map = f => x => x.map(f)

const join = x => y => y.join(x)


const digits = x => x < 10 ? '0' + x : x

const hours = x => Math.floor(x / 3600)

const minutes = x => Math.floor(x % 3600 / 60)

const seconds = x => Math.ceil(x % 3600 % 60)


const target = x => x.target

const delta = x => x.duration - x.currentTime

const number = x => isNaN(x) ? 0 : x

const data = x => y => x.data = y

const insert = x => y => y.parentNode.insertBefore(x, y)

const timer = f => x => x.ontimeupdate = f


const convert = list(hours, minutes, seconds)

const format = compose(map(digits), join(':'))

const calculate = compose(delta, number, convert, format)


const element = create('div')

const string = append(element, text(''))


const update = compose(calculate, data(string))

const display = compose(query(CONTAINER), insert(element))

const listen = compose(query(STREAM), timer(compose(target, update)))


element.style.cssText = 'display:flex;font-size:1.6rem;font-weight:400;line-height:2rem;color:#e91e63;'


window.addEventListener(PAGE, compose(target, display))

window.addEventListener(PLAYER, compose(target, listen))


Promise.resolve(document.body).then(display).catch(e => e)

Promise.resolve(document.body).then(listen).catch(e => e)