js添加删除二级菜单栏

<ul id="menu">
  <li>菜单1
    <ul class="submenu">
      <li>子菜单1.1</li>
      <li>子菜单1.2</li>
    </ul>
  </li>
  <li>菜单2</li>
</ul>
<button id="addBtn">添加二级菜单</button>
<button id="removeBtn">删除最后一个二级菜单</button>

document.getElementById('addBtn').addEventListener('click', addSubmenu);
document.getElementById('removeBtn').addEventListener('click', removeSubmenu);

function addSubmenu() {
  const menu = document.getElementById('menu');
  const lastLi = menu.lastElementChild;
  
  if (lastLi && lastLi.tagName === 'LI') {
    const submenu = document.createElement('ul');
    submenu.className = 'submenu';
    
    const newLi1 = document.createElement('li');
    newLi1.textContent = '新子菜单1';
    
    const newLi2 = document.createElement('li');
    newLi2.textContent = '新子菜单2';
    
    submenu.appendChild(newLi1);
    submenu.appendChild(newLi2);
    
    lastLi.appendChild(submenu);
  }
}

function removeSubmenu() {
  const menu = document.getElementById('menu');
  const lastLi = menu.lastElementChild;
  
  if (lastLi && lastLi.tagName === 'LI') {
    const submenu = lastLi.querySelector('.submenu');
    if (submenu) {
      lastLi.removeChild(submenu);
    }
  }
}