YouTube restore video time - ViolentMonkey user script

yt_restore_video_time.user.js

// ==UserScript==
// @name        YouTube restore video time
// @namespace   Violentmonkey Scripts
// @match       https://*.youtube.com/*
// @grant       none
// @version     1.0
// @author      mucaho
// @description -
// ==/UserScript==

var savedVideoTimePrefix = "SAVED_VIDEO_TIME_";

var player = document.getElementById("movie_player");
if (player) {
  
  player.addEventListener("onStateChange", onPlayerStateChange);
  function onPlayerStateChange(playerState) {
    var videoId, videoTime;
    
    if (playerState !== 1 /* YT.PlayerState.PLAYING */) return;
    if (player.getCurrentTime() > 1) return;
    if (!(videoId = player.getVideoData().video_id)) return;
    if (!(videoTime = +window.localStorage.getItem(savedVideoTimePrefix+videoId))) return;

    player.seekTo(videoTime, true);
  }
  
  window.addEventListener("beforeunload", function(evt) {
    var videoId, videoTime;
    
    if (!(videoId = player.getVideoData().video_id)) return;
    if (!(videoTime = player.getCurrentTime())) return;

    window.localStorage.setItem(savedVideoTimePrefix+videoId, ""+videoTime);
  });
}