Using a session variable to show a message once in Node.JS/Express

server.js

app.get('/', (req, res) => {
    var msg = req.session.message;
    req.session.message = undefined; // you must do it before rendering, instead it will just not work
    
    res.render('views/index.ejs', {
        message: msg
    });
})

.post('/connect', (req, res) => {
    // do some things :)
    
    req.session.message = {
        type: 'success', // to chose the color of the message in the view
        content: "Yay, you're connected!"
    };
    res.redirect('/');
});