hi 老师，
我正尝试使用socket.io来更新收到的notification .
但是这里我遇到一个问题，我需要把之前收到的消息都能够保存起来。我用的是TypeScript，然后以下的这段代码，我无论如何，notficationCount的list都为空。。能帮我看下是什么问题吗？谢谢！

前端 Client:
1.首先我把socket 用 useContext 装起来，便于全局使用：

import React from 'react';
import socketio from 'socket.io-client';


export const socket = socketio.connect(SOCKET_URL);
export const SocketContext = React.createContext();

2.接着，当我发送一个像点赞的消息之后，对方可以收到我的通知，备注的地方就是出问题的点，前端：

import {SocketContext} from '../../auth/context';
import React, {useEffect, useState, useContext, useLayoutEffect} from 'react';

const Home = () =>{
  const {socket, user} = useContext(SocketContext);
  const [notificationCount, setNotificationCount] = useState([]);
   const [me, setMe] = useState({});
     // init data
  const initialData = async () => {
    try {
      const meResult = await fetchGetMe();
      setMe(meResult?.data.data);
    } catch (error) {
      console.log('initial data发生错误：', error);
    }
  };
  useLayoutEffect(() => {
    initialData();
  }, []);
  //get feedback from socket
  useEffect(() => {
    socket.on('getNotification', data => {
      setNotificationCount(pre=> [...pre, data]); //就是这里出了问题。。
      console.log('现在获取到的notification data :', notificationCount);
    });

    return () => {
      socket.off('getNotification');
    };
  }, [socket]);

const onPressLike = ()=>{
   socket.emit('sendNotification', {
              senderUserId: me?.userId,
              senderName: me?.userName,
              receiverUserId: 123456, //我瞎编的，为了不让代码那么长..
              type: 0, // 0:like 1.gifts 2.sunflower
            });
}
<Button onClick={onPressLike}>点赞</Button>
}

后端的socket :

let onlineUsers = [];
const addUsers = (userId, socketId) => {
  !onlineUsers.some((m) => m.userId !== userId) &&
    onlineUsers.push({ userId, socketId });
};

const removeUser = (socketId) => {
  onlineUsers = onlineUsers.filter((user) => user.socketId !== socketId);
};

const getUser = (receiverId) => {
  return onlineUsers.find((m) => m.userId === receiverId);
};

io.on("connection", (socket) => {
  console.log("有人连接上了");
  socket.on("newUser", (userId) => {
    addUsers(userId, socket.id);
    console.log("现在的onlineUsers:", onlineUsers);
  });
  socket.on(
    "sendNotification",
    ({ senderUserId, senderName, receiverUserId, type }) => {
      console.log(
        `收到senderName:${senderName},receiverID:${receiverUserId};type:${type},socketId:${socket.id};senderUserId:${senderUserId}`
      );

      console.log("sendNotification之后，现在的onlineUsers:", onlineUsers);

      let receiver = {};
      if (onlineUsers.length > 0) {
        receiver = getUser(senderUserId);
        console.log("此时的receiver是：", receiver);
        io.to(receiver.socketId).emit("getNotification", {
          senderName,
          type,
        });
      } else {
        receiver = null;
        console.log("此时的receiver是：", receiver);
        socket.emit("getNotification", { receiver });
      }
    }
  );
  socket.on("disconnect", () => {
    console.log("有人下线了");
  });
});