幻灯片菜单布局返回左侧和内容视图的空引用

// 示例：React中的组件初始化
import React, { useEffect, useState } from 'react';

function App() {
  const [menuItems, setMenuItems] = useState([]);
  const [content, setContent] = useState(null);

  useEffect(() => {
    // 模拟异步加载菜单项
    fetchMenuItems().then(items => setMenuItems(items));
  }, []);

  const handleMenuItemClick = (item) => {
    // 模拟异步加载内容
    fetchContent(item.id).then(data => setContent(data));
  };

  return (
    <div>
      <Menu items={menuItems} onClick={handleMenuItemClick} />
      {content && <ContentView data={content} />}
    </div>
  );
}

function ContentView({ data }) {
  if (!data) {
    return <div>Loading...</div>;
  }
  return (
    <div>
      {/* 渲染内容 */}
    </div>
  );
}

// 示例：Redux中的状态更新
const initialState = {
  menuItems: [],
  content: null
};

function reducer(state = initialState, action) {
  switch (action.type) {
    case 'SET_MENU_ITEMS':
      return { ...state, menuItems: action.payload };
    case 'SET_CONTENT':
      return { ...state, content: action.payload };
    default:
      return state;
  }
}

// 示例：使用querySelector检查元素是否存在
const element = document.querySelector('.content-view');
if (element) {
  // 操作元素
}