当单击另一个父级时隐藏父级的子菜单内容

<ul class="menu">
  <li class="parent">
    <a href="#">父级菜单1</a>
    <ul class="submenu">
      <li><a href="#">子菜单1</a></li>
      <li><a href="#">子菜单2</a></li>
      <li><a href="#">子菜单3</a></li>
    </ul>
  </li>
  <li class="parent">
    <a href="#">父级菜单2</a>
    <ul class="submenu">
      <li><a href="#">子菜单4</a></li>
      <li><a href="#">子菜单5</a></li>
      <li><a href="#">子菜单6</a></li>
    </ul>
  </li>
</ul>

.submenu {
  display: none;
}

.parent.active .submenu {
  display: block;
}

var parents = document.querySelectorAll('.parent');

parents.forEach(function(parent) {
  parent.addEventListener('click', function() {
    // 切换active类
    this.classList.toggle('active');
    
    // 隐藏其他父级菜单的子菜单
    var siblings = this.parentNode.children;
    for (var i = 0; i < siblings.length; i++) {
      if (siblings[i] !== this) {
        siblings[i].classList.remove('active');
      }
    }
  });
});