优化React useEffect实现用户资料实时更新

useEffect(() => {
    const data = getUser2().then((res) => {
      setUserData({
        firstName: res.firstName,
        lastName: res.lastName,
        email: res.email,
        phoneNumber: res.phoneNumber,
        location: res.location,
      });
    });
    return () => data; // 错误：data是一个Promise，不是清理函数
  }, [userData]); // 问题：依赖于userData，可能导致无限循环或不及时更新

import React, { createContext, useState, useEffect, useContext } from 'react';
// 假设 useUserContext 和 getUser2 是已经定义的函数
// import { useUserContext } from './UserContext'; // 假设的用户上下文
// import { getUser2 } from './api'; // 假设的API调用

const UserDetailsContext = createContext();

export function UserDetailsProvider({ children }) {
  const { user, setUser } = useUserContext(); // 从用户上下文中获取用户状态
  const [userData, setUserData] = useState({
    firstName: "",
    lastName: "",
    email: "",
    phoneNumber: "",
    location: "",
  });

  useEffect(() => {
    let isMounted = true; // 用于防止在组件卸载后更新状态

    // 只有当user存在（即用户已登录）时才尝试获取用户资料
    if (user) {
      console.log("Fetching user details for:", user); // 调试信息
      getUser2()
        .then((res) => {
          if (isMounted) { // 确保组件仍然挂载
            setUserData({
              firstName: res.firstName,
              lastName: res.lastName,
              email: res.email,
              phoneNumber: res.phoneNumber,
              location: res.location,
            });
          }
        })
        .catch((err) => {
          if (isMounted) {
            console.error("Failed to fetch user details:", err);
            // 可以在此处处理错误，例如清空userData或显示错误消息
            setUserData({
                firstName: "", lastName: "", email: "",
                phoneNumber: "", location: ""
            });
          }
        });
    } else {
      // 用户未登录或已登出，清空用户资料
      if (isMounted) {
        setUserData({
          firstName: "",
          lastName: "",
          email: "",
          phoneNumber: "",
          location: "",
        });
      }
    }

    return () => {
      isMounted = false; // 清理函数：组件卸载时设置标志
    };
  }, [user]); // 关键：依赖于user对象，当user改变时重新运行效果

  return (
    <UserDetailsContext.Provider value={{ userData, setUserData }}>
      {children}
    </UserDetailsContext.Provider>
  );
}

export function useUserDetails() {
  return useContext(UserDetailsContext);
}

// App.js
import { useEffect, useState } from 'react';
import { useNavigate } from 'react-router-dom';
// import { getUser } from './api'; // 假设的API调用，用于获取username

export default function App() {
  const route = useNavigate();
  const [user, setUser] = useState(null); // 这里的user可能只是一个username字符串

  useEffect(() => {
    const unsubscribe = getUser() // 假设getUser返回一个Promise
      .then((res) => {
        if (res.error) {
          console.log(res.error);
          setUser(null); // 错误时清空user
        } else {
          setUser(res.username); // 成功时设置username
        }
      })
      .catch((err) => {
        console.log(err);
        setUser(null); // 错误时清空user
      });
    // 如果getUser返回的是一个可取消的订阅，这里可以返回取消函数
    // return () => unsubscribe(); 
    // 对于Promise，通常不需要特殊的清理，除非你在Promise解决前卸载了组件
  }, []); // 依赖项为空数组，只在组件挂载时运行一次

  // ... App的其他逻辑和路由
}

// Controller:
exports.getLoggedInUser = (req, res) => {
  // req.user 应该由认证中间件填充，包含当前登录用户的信息
  if (!req.user) {
    return res.status(401).json({ message: "User not authenticated" });
  }
  return res.status(200).json({
    message: "User is still logged in",
    firstName: req.user.firstName,
    lastName: req.user.lastName,
    email: req.user.email,
    location: req.user.location,
    phoneNumber: req.user.phoneNumber,
    username: req.user.username,
  });
};