Detect and fill checkboxes in checkout flow for Ontario Parks Reservations.

OntarioParksReservation-2-Checkboxes.user.js

// ==UserScript==
// @name         OntarioParksReservation-2-Checkboxes
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Detect and fill checkboxes in checkout flow
// @author       You
// @match        https://reservations.ontarioparks.com/Messages.aspx
// @match        https://reservations.ontarioparks.com/Account/Auth/Payment.aspx
// @require      https://greasyfork.org/scripts/12228/code/setMutationHandler.js
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // Your code here...
    // maybe the elements are already on the page
    checkThem([].slice.call(document.querySelectorAll('input[type="checkbox"]')));

    // but anyway set a MutationObserver handler for them
    setMutationHandler(document, 'input[type="checkbox"]', checkThem);

    function checkThem(nodes) {
        nodes.forEach(function(n) { n.checked = true });
    }

    // click Continue
    document.querySelector('#MainContentPlaceHolder_ContinueButton').click()

})();