Display subtitle while pressing S key in YouTube.

keytosubtitles.user.js

// ==UserScript==
// @name         Key to Subtitles
// @namespace    https://github.com/kusaanko
// @version      0.1
// @description  Display subtitle while pressing S key in YouTube.
// @author       Kusaanko
// @match        https://www.youtube.com/watch*
// @grant        none
// @require      https://code.jquery.com/jquery-3.3.1.min.js
// ==/UserScript==

(function() {
    document.onkeydown = function(e) {
        if(document.activeElement.nodeName!='INPUT'&&e.keyCode==83&&$('.ytp-subtitles-button.ytp-button').attr('aria-pressed')=='false') {
            $('.ytp-subtitles-button.ytp-button').click();
        }
    }
    document.onkeyup = function(e) {
        if(!document.activeElement.nodeName!='INPUT'&&e.keyCode==83&&$('.ytp-subtitles-button.ytp-button').attr('aria-pressed')=='true') {
            $('.ytp-subtitles-button.ytp-button').click();
        }
    }
})();