Express.js: Working with Sessions and Cookies

In this article, we’ll explore how to manage sessions and cookies in an Express.js application. Sessions and cookies are essential for preserving user data across multiple HTTP requests and for maintaining user authentication.

Understanding Sessions and Cookies

Cookies: Small pieces of data stored on the client’s browser. They can be used to store information such as user preferences and session IDs.
Sessions: Server-side storage of user data. Sessions use a unique identifier (session ID) stored as a cookie on the client to track data stored on the server.

Setting Up Express Session Management

To work with sessions in Express, we’ll use the express-session package.

Step 1: Install `express-session`

First, install the express-session package in your project:

npm install express-session

Step 2: Configure Session Middleware

Add the session middleware to your Express application to set up sessions.

import express from 'express';
import session from 'express-session';

const app = express();
const PORT = 3000;

// Session middleware configuration
app.use(session({
    secret: 'your_secret_key', // Replace with a strong secret in production
    resave: false,
    saveUninitialized: true,
    cookie: { secure: false } // Set to true if using HTTPS
}));

Step 3: Storing and Accessing Session Data

To store data in a session, assign it to the req.session object. Let’s create a route that stores a user ID in the session upon login.

app.post('/login', (req, res) => {
    // Simulate user login
    req.session.userId = 1; // Typically, this would be fetched from a database
    res.send('User logged in, session data stored');
});

To retrieve session data, access req.session in other routes:

app.get('/profile', (req, res) => {
    if (req.session.userId) {
        res.send(`User profile for user ID: ${req.session.userId}`);
    } else {
        res.send('User not logged in');
    }
});

Step 4: Destroying Sessions

To log a user out, destroy the session data:

app.post('/logout', (req, res) => {
    req.session.destroy((err) => {
        if (err) {
            return res.status(500).send('Error logging out');
        }
        res.send('User logged out, session destroyed');
    });
});

Working with Cookies

Express has a built-in way to set cookies. Let’s set a cookie with a user’s preferred theme.

Setting Cookies

Use res.cookie() to set a cookie:

app.get('/set-theme', (req, res) => {
    res.cookie('theme', 'dark', { maxAge: 900000, httpOnly: true });
    res.send('Theme cookie set');
});

Accessing Cookies

Use req.cookies to access cookies. For this, we’ll need the cookie-parser middleware.

Install cookie-parser:
```
 npm install cookie-parser
```

Configure it in your app:

 import cookieParser from 'cookie-parser';

 app.use(cookieParser());

 app.get('/get-theme', (req, res) => {
     const theme = req.cookies.theme || 'default';
     res.send(`Current theme: ${theme}`);
 });

Clearing Cookies

To delete a cookie, use res.clearCookie():

app.get('/clear-theme', (req, res) => {
    res.clearCookie('theme');
    res.send('Theme cookie cleared');
});