focused_youtube.js

// ==UserScript==
// @name         Focused YouTube
// @namespace    http://tampermonkey.net/
// @version      1.0
// @description  Remove distracting things (comments, other video suggestions) from YouTube video pages
// @author       Nathan Hunt
// @match        https://www.youtube.com/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict'

    let waitAndHide = function(id) {
        setTimeout(function () {
            let element = document.getElementById(id)
            console.log(`Trying to hide ${id} (${element}).`)
            if (element) {
                element.style.display = 'none'
            } else {
                waitAndHide(id)
            }
        }, 1000)
    }
    waitAndHide('comments')
    // the videos on the side, including Up Next
    waitAndHide('items')
})()