To implement Express Session in a Node.js application, you need to follow these steps:

Install the necessary dependencies:

First install Express Session:

npm install express express-session

Require the ‘express’ and ‘express-session’ modules in your Node.js application:

const express = require('express');
const session = require('express-session');

Set up the Express app and configure the session middleware.

You need to use ‘express-session’ middleware before setting up your routes:

const app = express();

app.use(session({
    secret: 'your_secret_key', // Change this to your own secret
    resave: false,
    saveUninitialized: true
}));

• secret: This is a string used to sign the session ID cookie. You should change it to a random string.
• resave: Forces the session to be saved back to the session store, even if the session was never modified during the request.
• saveUninitialized: Forces a session that is “uninitialized” to be saved to the store. A session is uninitialized when it is new but not modified.

You can now access and modify the session object in your routes. Here’s an example of a route that sets a session variable and retrieves it:

app.get('/setSession', (req, res) => {
    req.session.username = 'user123';
    res.send('Session variable set');
});

app.get('/getSession', (req, res) => {
    const username = req.session.username;
    res.send('Session variable: ' + username);
});

In this example, /setSession sets the username session variable to 'user123', and /getSession retrieves it.

Start the Express server

const port = 3000;
app.listen(port, () => {
    console.log(`Server is listening on port ${port}`);
});

Make sure to handle session persistence properly, as it can be crucial for maintaining user authentication and state across requests.