Google Calendar Guests Can Modify Event By Default (port to TamperMonkey)

user.js

// ==UserScript==
// @name         Google Calendar Guests Can Modify Event By Default
// @namespace    http://tampermonkey.net/
// @version      0.4
// @updateURL    https://gist.githubusercontent.com/mwek/9962f97f3bde157fd5dbd2b5dd0ec3ca/raw/user.js
// @description  Enables 'Guests can modify event' setting for google calendar by default, when creating a new event.
// @author       Robin Drexler
// @match        https://calendar.google.com/*
// @match        https://www.google.com/calendar/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    function onLoad() {
        // checkbox id is generated dynamically, so let's find it by ARIA label ¯\_(ツ)_/¯
        var modifyEventCheckbox = document.querySelector('div[aria-label="Let guests modify the event"]');
        var clickEvent = new MouseEvent("click", {
            bubbles: true,
            cancelable: true,
            view: window
        });

        if (!!modifyEventCheckbox && modifyEventCheckbox.getAttribute('aria-checked') != "true") {
            // activate the checkbox by mimicing click
            modifyEventCheckbox.dispatchEvent(clickEvent);
        }
    }

    window.addEventListener('pageshow', function() {
        // delay execution, because DOM might not be ready immediately
        // after event was fired
        window.setTimeout(onLoad, 250);
    });
    onLoad();
})();