DisableYoutube0to9Hotkeys.user.js

// ==UserScript==
// @name         Disable Youtube 0-9 Hotkeys
// @namespace    http://tampermonkey.net/
// @version      0.1.1
// @description  Disables Youtube 0-9 hotkeys.
// @author       Zack (Gkjsdll) Winchell
// @icon         https://www.youtube.com/s/desktop/b7e72d39/img/favicon_144.png
// @match        *://www.youtube.com/*
// @match        *://m.youtube.com/*
// @grant        none
// ==/UserScript==

const targetIsInput = (event) => {
  const { target: { isContentEditable, tagName } } = event;

  const inputTagNames = ['INPUT', 'SELECT', 'TEXTAREA'];

  if (inputTagNames.includes(tagName)) {
    return true;
  }

  if (isContentEditable) {
    return true;
  }

  return false;
}

const kaydownHandler = (event) => {
  const { key, target: { isContentEditable, tagName } } = event;

  // Don't prevent entering numbers in input areas
  if (targetIsInput(event)) {
    return;
  }

  // Trap number keys
  if (key >= '0' && key <= '9') {
    event.stopImmediatePropagation();
  }
}

window.addEventListener('keydown', kaydownHandler, true);