/** @type {HTMLElement} */ const header = document.querySelector('body > header'); /** @type {HTMLButtonElement} */ const toggleButton = document.querySelector('button#mobile-menu'); function toggleNavbar() { const present = header.classList.toggle('collapsed'); if (present) { header.setAttribute('aria-expanded', 'true'); } else { header.setAttribute('aria-expanded', 'false'); } } toggleButton.addEventListener('click', toggleNavbar);