paper-dropdown-动态添加菜单项时菜单的标签不会更新

<paper-dropdown-menu label="选择菜单项">
  <paper-listbox id="menuItems" slot="dropdown-content">
    <paper-item>菜单项1</paper-item>
    <paper-item>菜单项2</paper-item>
  </paper-listbox>
</paper-dropdown-menu>

<script>
  // 获取菜单和菜单项
  const dropdown = document.querySelector('paper-dropdown-menu');
  const menuItems = document.querySelector('#menuItems');

  // 动态添加菜单项的函数
  function addMenuItem(label) {
    const item = document.createElement('paper-item');
    item.textContent = label;
    menuItems.appendChild(item);

    // 更新菜单标签的数据
    dropdown.label = label;

    // 更新菜单的显示
    dropdown.updateLabelVisibility();
  }

  // 示例调用
  addMenuItem('菜单项3');
</script>