youtube-old-layout.js

// This script is not mine. For source look into here:
// https://cable.ayra.ch/tampermonkey/view.php?script=youtube_old_design.user.js
(function () {
    var getDesignCookie = function (cookie) {
        //Find existing preferences
        var prefs = cookie.split("; ").filter(function (v) {
                return v.indexOf("PREF=") === 0;
            })[0];
        //No preferences, return new ones with design setting
        if (!prefs) {
            console.log("prefs not set in cookie");
            return "PREF=f6=8";
        }
        //Process all settings
        var entries = prefs.substr(5).split('&');
        var set = false;
        for (var i = 0; i < entries.length; i++) {
            if (entries[i].indexOf("f6=") === 0) {
                set = true;
                //Set the old design flag
                var value = +entries[i].substr(3);
                if ((value & 8) === 0) {
                    console.log("Activating old design and reloading...");
                    entries[i] = "f6=" + (value | 8);
                    window.setTimeout(location.reload.bind(location,true),100);
                }
                else{
                    console.log("Old design already active. Doing nothing");
                }
            }
        }
        //Design flag setting doesn't exists. Adding it instead
        if (!set) {
            console.log("Activating old design and reloading...");
            entries.push("f6=8");
            window.setTimeout(location.reload.bind(location,true),100);
        }
        //Build cookie
        return "PREF=" + entries.join('&');
    };
    //Update cookie
    document.cookie = getDesignCookie(document.cookie) + ";domain=.youtube.com;path=/";
})();