Express.js Interview Questions and Answers (2025)

Express JS Interview Questions and Answers For Intermediate

22. What is the difference between res.send() and res.json() in Express.js?

res.send() is used to send a response with any type of data (string, object, buffer, etc.). While res.json() is used to send a JSON response. res.json() also sets the Content-Type header to application or JSON.

23. What is the use of app.use() in Express.js?

app.use() is used to add middleware functions to an Express application. It can be used to add global middleware functions or to add middleware functions to specific routes.

24. What is the purpose of the next() function in Express.js?

The next() function is used to pass control from one middleware function to the next function. It is used to execute the next middleware function in the chain.

25. What is the difference between app.route() and app.use() in Express.js?

app.route() defines multiple route handlers for a single route. While the app.use() function is used to add middleware functions to an application.

26. What is the purpose of the req.params object in Express.js?

The req.params object is used to access route parameters in Express.js. Route parameters capture values from the URL and pass them to the request handler.

27. What is the difference between req.query and req.params in Express.js?

req.query is used to access the query parameters in a URL. While req.params is used to access route parameters in a URL.

28. What is the purpose of the app.locals object in Express.js?

The app.locals object stores application-level data in an Express.js application. This data is available to all templates and routes.

29. How do you perform URL redirection in Express.js?

Use the res.redirect() method:

res.redirect('/home');

30. How can you set cookies in Express.js?

Use the res.cookie() method:

res.cookie('username', 'John');

31. How can you delete cookies in Express.js?

Use the res.clearCookie() method:

res.clearCookie('username');

32. What is app.all() used for in Express.js?

The app.all() method is used to handle all HTTP methods for a specific route.

33. How do you handle 404 errors in Express.js?

Create middleware at the end of the route handlers:

app.use((req, res) => {
  res.status(404).send('Page Not Found');
});

34. What is app.set() used for in Express.js?

The app.set() method is used to set application-level properties like view engine or port.

35. How do you handle JSON data in Express.js?

Use the express.json() middleware:

app.use(express.json());

36. What is the difference between app.locals and res.locals?

• app.locals: Application-level data shared across all requests.
• res.locals: Request-specific data available only in the current request.

37. How do you define route groups in Express.js?

Route groups can be defined using express.Router().

const router = express.Router();
router.get('/users', (req, res) => res.send('User List'));
app.use('/api', router);

38. How can you serve dynamic content using Express.js?

Use template engines like EJS or Pug with Express.js.

Express JS Interview Questions and Answers For Advanced

39. How do you implement JWT-based authentication in Express.js?

Use the jsonwebtoken package:

const jwt = require('jsonwebtoken');
jwt.sign({ id: user.id }, 'secretKey', { expiresIn: '1h' });

40. How can you perform request validation in Express.js?

Use the express-validator middleware:

const { check, validationResult } = require('express-validator');
app.post('/user', [check('email').isEmail()], (req, res) => {
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    return res.status(400).json({ errors: errors.array() });
  }
});

41. How do you upload files using Multer in Express.js?

const multer = require('multer');
const upload = multer({ dest: 'uploads/' });
app.post('/upload', upload.single('file'), (req, res) => {
  res.send('File uploaded');
});

42. How can you implement rate limiting in Express.js?

Use the express-rate-limit package:

const rateLimit = require('express-rate-limit');
const limiter = rateLimit({ windowMs: 15 * 60 * 1000, max: 100 });
app.use(limiter);

43. How do you implement pagination in Express.js with MongoDB?

Use skip() and limit() methods:

Model.find().skip(page * limit).limit(limit);

44. How do you encrypt passwords in Express.js?

Use the bcrypt package:

const bcrypt = require('bcrypt');
bcrypt.hash('password', 10, (err, hash) => console.log(hash));

45. How can you handle CORS in Express.js?

Use the cors middleware:

const cors = require('cors');
app.use(cors());

46. How do you log HTTP requests in Express.js?

Use the morgan middleware:

const morgan = require('morgan');
app.use(morgan('tiny'));

47. How can you schedule jobs in Express.js?

Use the node-cron package:

const cron = require('node-cron');
cron.schedule('* * * * *', () => console.log('Job running every minute'));

48. How do you integrate MySQL with Express.js?

Use the mysql2 package:

const mysql = require('mysql2');
const db = mysql.createConnection({ host: 'localhost', user: 'root', database: 'test' });
db.connect();

49. How can you generate API documentation in Express.js?

Use Swagger with Express.js.

50. How do you handle multiple database connections in Express.js?

Create separate mongoose instances for each connection.

51. How can you implement Socket.IO with Express.js?

Integrate socket.io with Express.js for real-time applications.

Frequently Asked Questions

What is an express JS interview?

An Express.js interview is an interview for a job that involves using Express.js. During the interview, the interviewer will likely ask about your experience with Express.js and web development.

Why is express JS better?

Express Js is better because it is lightweight and fast, has a Flexible routing system, supports a large number of middleware modules, has strong community and support, and has easy integration with other technologies.

What is ExpressJS used for?

Express.js is a server-side JavaScript framework used for building web applications. For Example, RESTful APIs, server-side web applications, handling HTTP requests, and integrating with databases.

Conclusion

In conclusion, preparing for an Express.js interview can be hard. With the proper knowledge and practice, you can prepare easily. Express.JS interview questions and answers in this article will help you prepare. 

Recommended Readings:

• Express JS vs Node JS
• Introduction to Express
• Setting up Express.js
• CRUD in Express