Tampermonkey: YouTube: scroll=seek in fullscreen

youtube-fullscreen-seek.js

// ==UserScript==
// @name         YouTube: scroll=seek in fullscreen
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Scrolling a youtube video in fullscreen seeks back/forward
// @author       Ralf Vogler
// @match        https://www.youtube.com/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // seek back/forward `step` seconds
    const step = 3;

    // This should work for any video, so maybe generalize it...
    // However, for performance reasons we should then abort if there's no video element and add/remove the wheel listener on fullscreenchange.

    const v = document.getElementsByTagName('video')[0];
    document.addEventListener('wheel', function(e){
        // const dir = e.wheelDeltaY > 0 ? 'up' : 'down';
        // console.log("wheel", dir);
        if(document.webkitIsFullScreen) { // https://developer.mozilla.org/en-US/docs/Web/API/Fullscreen_API#Prefixing
            // console.log("fullscreen");
            v.currentTime += step * Math.sign(e.wheelDeltaY);
        }
    });
})();