responsive drop down menu with submenu w3school code example

Example: Responsive drop down menu with submenu

/* Activate Submenu */
function toggleItem() {
  if (this.classList.contains("submenu-active")) {
    this.classList.remove("submenu-active");
  } else if (menu.querySelector(".submenu-active")) {
    menu.querySelector(".submenu-active").classList.remove("submenu-active");
    this.classList.add("submenu-active");
  } else {
    this.classList.add("submenu-active");
  }
}
 
/* Event listeners */
for (let item of items) {
    if (item.querySelector(".submenu")) {
      item.addEventListener("click", toggleItem, false);
    }   
}