我看了一个关于使用Reaction和Firebase的实时聊天室的教程.下面的代码是AuthContext文件，有人能解释一下useEffect的部分吗，为什么清理函数只是unSub()？
import { createContext, useEffect, useState } from "react";
import { auth } from "../firebase";
import { onAuthStateChanged } from "firebase/auth";
export const AuthContext = createContext();
export const AuthContextProvider = ({ children }) => {
const [currentUser, setCurrentUser] = useState({});
useEffect(() => {
const unsub = onAuthStateChanged(auth, (user) => {
setCurrentUser(user);
console.log(user);
});
return () => {
unsub();
};
}, []);
return (
<AuthContext.Provider value={{ currentUser }}>
{children}
</AuthContext.Provider>
);
};
我试着在网上找到解决方案，但并不是真正相关