可伸缩关闭的js菜单

<ul class="menu">
  <li>
    <a href="#" class="menu-item">菜单项 1</a>
    <ul class="submenu">
      <li><a href="#">子菜单项 1.1</a></li>
      <li><a href="#">子菜单项 1.2</a></li>
    </ul>
  </li>
  <li>
    <a href="#" class="menu-item">菜单项 2</a>
    <ul class="submenu">
      <li><a href="#">子菜单项 2.1</a></li>
      <li><a href="#">子菜单项 2.2</a></li>
    </ul>
  </li>
</ul>

.menu {
  list-style: none;
  padding: 0;
}

.menu-item {
  display: block;
  padding: 10px;
  background-color: #f1f1f1;
  cursor: pointer;
}

.submenu {
  display: none;
  list-style: none;
  padding-left: 20px;
}

.submenu li a {
  display: block;
  padding: 8px;
}

document.addEventListener('DOMContentLoaded', function() {
  const menuItems = document.querySelectorAll('.menu-item');

  menuItems.forEach(item => {
    item.addEventListener('click', function(e) {
      e.preventDefault();
      const submenu = this.nextElementSibling;
      if (submenu.style.display === 'block') {
        submenu.style.display = 'none';
      } else {
        submenu.style.display = 'block';
      }
    });
  });
});

.submenu {
  display: none;
  transition: max-height 0.3s ease-out;
  max-height: 0;
  overflow: hidden;
}

.menu-item.active + .submenu {
  display: block;
  max-height: 500px; /* 设置一个足够大的值 */
}

item.addEventListener('click', function(e) {
  e.preventDefault();
  // 其他代码...
});