const sessionMiddleware = expressSession({
    secret: 'Tecky Academy teaches typescript',
    resave:true,
    saveUninitialized:true,
    cookie:{secure:false}
});

app.use(sessionMiddleware);

io.use((socket,next)=>{
    let req = socket.request as express.Request
    let res = req.res as express.Response
    sessionMiddleware(req, res, next as express.NextFunction
});
//...
io.on('connection', function (socket) {
    // You can set any values you want to session here.
    const req = socket.request as express.Request;
    req.session['key'] = 'XXX';
    // There is no auto save for session.
    socket.request.session.save();

    // You can also send data using socket.emit() although it is not very useful
    socket.emit('any-key','values');
    socket.on("disconnect",()=>{
        //... rest of the code
    })
});