js二级纵向菜单

<ul class="menu">
  <li>
    <a href="#">菜单1</a>
    <ul class="submenu">
      <li><a href="#">子菜单1-1</a></li>
      <li><a href="#">子菜单1-2</a></li>
    </ul>
  </li>
  <li>
    <a href="#">菜单2</a>
    <ul class="submenu">
      <li><a href="#">子菜单2-1</a></li>
      <li><a href="#">子菜单2-2</a></li>
    </ul>
  </li>
</ul>

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

.menu > li {
  position: relative;
}

.menu a {
  display: block;
  padding: 10px;
  text-decoration: none;
  color: #333;
}

.submenu {
  display: none;
  position: absolute;
  top: 0;
  left: 100%;
  background-color: #fff;
  border: 1px solid #ccc;
  list-style-type: none;
  padding: 0;
  min-width: 150px;
}

.menu > li:hover .submenu {
  display: block;
}

document.querySelectorAll('.menu > li').forEach(function(li) {
  li.addEventListener('click', function(event) {
    event.stopPropagation();
    this.querySelector('.submenu').classList.toggle('active');
  });
});