How to get hold messages from socket.io when a socket reconnects

Question

I'm creating a chat function for a flutter application. I'm using socket.io version 2 because it is the stable version with socket.io-client-dart

My chat functions are working fine. My problem is if one person disconnected between a chat and connect back after how he can get the messages that came to him between the disconnection.

here is my code.

const express = require("express");
var http = require("http");
const app = express();
const port = process.env.PORT || 5000;
var server = http.createServer(app);

var io = require("socket.io")(server);

var clients = {};

io.on("connection", (socket) => {
  console.log("connetetd");

  socket.on("signin", (user_id) => {
    clients[user_id] = socket.id;
  });
  
  socket.on("message", (msg) => {
    console.log("user-messaging")
  
    socket.to(clients[msg.targetId]).emit("message", msg)

  });

  socket.on("disconnect", () => {
    console.log("disconnected from soket - ",socket.id);
  });

});

server.listen(port, "0.0.0.0", () => {
  console.log("Socket server started in port -" + port);
});