google-account-autoswitcher.js

// ==UserScript==
// @name         Google Account Auto Switcher
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You

// @match        https://calendar.google.com/calendar/u/0/*
// @match        https://drive.google.com/drive/u/0/*
// @match        https://mail.google.com/mail/u/0/*

// @icon         https://www.google.com/s2/favicons?sz=64&domain=google.com
// @grant        none
// @run-at       document-start
// @noframes
// ==/UserScript==

(async function () {
  "use strict";

  const targetAccountNumber = 1;

  const url = new URL(window.location.href);

  url.pathname = url.pathname.replace(
    /\/u\/\d+\//,
    `/u/${targetAccountNumber}/`,
  );

  window.location.replace(url);
})();