menu-responsivo.html

<!-- Definición del menú -->
<nav class="navbar navbar-expand-md navbar-dark bg-dark fixed-top">
    <a class="navbar-brand" target="_blank" href="//parzibyte.me/blog">Node y MySQL - By Parzibyte</a>
    <button aria-label="Mostrar u ocultar menú" class="navbar-toggler" id="botonMenu" type="button">
        <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse" id="menu">
        <ul class="navbar-nav mr-auto">
            <li class="nav-item">
                <a class="nav-link" href="/productos">Ver</a>
            </li>
            <li class="nav-item">
                <a class="nav-link" href="/productos/agregar">Agregar</a>
            </li>
        </ul>
    </div>
</nav>
<script type="text/javascript">
    // Tomado de https://github.com/parzibyte/cotizaciones_web/blob/master/js/cotizaciones.js#L2
    document.addEventListener("DOMContentLoaded", () => {
        const menu = document.querySelector("#menu"),
            botonMenu = document.querySelector("#botonMenu");
        if (menu) {
            botonMenu.addEventListener("click", () => menu.classList.toggle("show"));
        }
    });
</script>