如何将可折叠面板的状态保存到会话变量？

// 监听可折叠面板状态变化事件
document.getElementById('panel').addEventListener('click', function() {
  var panelState = this.classList.contains('expanded') ? 'expanded' : 'collapsed';
  
  // 将面板状态保存到会话变量
  sessionStorage.setItem('panelState', panelState);
});

// 恢复面板状态
window.addEventListener('load', function() {
  var panelState = sessionStorage.getItem('panelState');
  
  if (panelState === 'expanded') {
    // 展开面板
    document.getElementById('panel').classList.add('expanded');
  } else {
    // 折叠面板
    document.getElementById('panel').classList.remove('expanded');
  }
});