Displaying User's ID in bottom of control panel(Vanilla JS).
Per
// ==UserScript==
// @name Greasy Fork Display User's ID
// @namespace -
// @version 0.2
// @description Displaying User's ID in bottom of control panel(Vanilla JS).
// @author NotYou
// @match *greatest.deepsurf.us/*/users/*
// @license GPLv3
// @license-link https://www.gnu.org/licenses/gpl-3.0.txt
// @grant none
// ==/UserScript==
const userID = window.location.pathname.substring(10)
const createElem = document.createElement("span");
const textNode = document.createTextNode(" [ User ID: " + userID + " ]");
createElem.appendChild(textNode);
const elem = document.getElementById("about-user");
elem.appendChild(createElem);