document.addEventListener("DOMContentLoaded", () => {

    let dropdownmenuElement = document.getElementById("dropdownmenu");
    let dropdownmenuButtonElement = document.getElementById("dropdownmenu-button");

    if (dropdownmenuButtonElement != null) {

        dropdownmenuButtonElement.addEventListener("click", () => {

            if (dropdownmenuElement.classList.contains("dropdownvisible")) {
                dropdownmenuElement.classList.remove("dropdownvisible");
            }
            else {
                dropdownmenuElement.classList.add("dropdownvisible");
            }

        })

    }

})