Cookies and sessions are two ways to persist data in a web application. Cookies are small pieces of data that are stored on the client-side and sent with each request to the server, while sessions are stored on the server-side and a session ID is sent to the client to identify the session.

Express.js provides middleware for working with cookies and sessions. Here's an overview of how to use them:

Cookies

To use cookies in Express.js, you can use the cookie-parser middleware. Here's an example of how to set a cookie:

Notes

Need To install the cookie-parser middleware for Express.js, you can use the npm package manager. Here's an example:

npm install cookie-parser

const express = require("express");
const cookieParser = require("cookie-parser");

const app = express();

app.use(cookieParser());

app.get("/", (req, res) => {
  res.cookie("name", "value");
  res.send("Cookie set");
});

app.listen(3000, () => {
  console.log("Server listening on port 3000");
});

In the above example, the cookie-parser middleware is added to the application using app.use(cookieParser()). The res.cookie() method is used to set a cookie with the name name and the value value.

To read a cookie, you can use the req.cookies object. Here's an example:

app.get("/", (req, res) => {
  const name = req.cookies.name;
  res.send(`Cookie value: ${name}`);
});

In the above example, the name variable is assigned the value of the name cookie using req.cookies.name.

Sessions

To use sessions in Express.js, you can use the express-session middleware. Here's an example of how to set up sessions:

Notes

Need To install the express-session middleware for Express.js, you can use the npm package manager. Here's an example:

npm install express-session

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

const app = express();

app.use(
  session({
    secret: "mysecret",
    resave: false,
    saveUninitialized: true,
  })
);

app.get("/", (req, res) => {
  req.session.name = "value";
  res.send("Session set");
});

app.listen(3000, () => {
  console.log("Server listening on port 3000");
});

In the above example, the express-session middleware is added to the application using app.use(session(options)). The options object is used to configure the session, including a secret key for encrypting the session data.

To read a session value, you can use the req.session object. Here's an example:

app.get("/", (req, res) => {
  const name = req.session.name;
  res.send(`Session value: ${name}`);
});

In the above example, the name variable is assigned the value of the name session variable using req.session.name.

Error handling can also be implemented for cookies and sessions, as well as data validation.