If you’re preparing for a web development interview or aiming to land a Node.js developer role, mastering Express.js is essential.

As one of the most popular Node.js frameworks, Express.js simplifies building robust web applications and APIs. In this post, we have compiled the top 25 Express.js interview questions with detailed explanations and practical examples to help you confidently tackle technical interviews.

Whether you’re a fresher or an experienced developer brushing up on your knowledge, these questions will give you a clear understanding of key Express.js concepts, best practices, and coding patterns used in real-world scenarios.

1. What is Express.js?

Express.js is a fast, unopinionated, minimalist web framework for Node.js that helps developers build web applications and APIs easily.

Example:

const express = require(‘express’);

const app = express();

app.get(‘/’, (req, res) => {

    res.send(‘Hello World!’);

});

app.listen(3000);

2. What are the features of Express.js?

• Middleware support.

   

• Routing.

   

• Templating engine support.

   

• HTTP utilities.

   

• Error handling.

   

• Support for REST APIs.

   

3. What is middleware in Express.js?

Middleware are functions that execute during the request-response cycle. They have access to req, res, and next().

Example:

app.use((req, res, next) => {

    console.log(‘Request URL:’, req.url);

    next();

});

4. Explain the routing in Express.js?

Routing defines how an app responds to client requests.

Example:

app.get(‘/user’, (req, res) => {

    res.send(‘GET user’);

});

5. What are different HTTP methods supported by Express.js?

• GET

   

• POST

   

• PUT

   

• DELETE

   

• PATCH

   

• OPTIONS

   

• HEAD

   

6. What is the purpose of next() in middleware?

next() passes control to the next middleware or route handler.

7. How to handle errors in Express.js?

Error-handling middleware has four arguments: err, req, res, next.

Example:

app.use((err, req, res, next) => {

    console.error(err.stack);

    res.status(500).send(‘Something broke!’);

});

8. What is app.use()?

It mounts middleware at the specified path. If no path is specified, it defaults to ‘/’.

9. Difference between app.use() and app.get()?

• app.use() applies middleware for all requests.

   

• app.get() handles GET requests for a specific path.

   

10. How can you serve static files using Express.js?

Use express.static() middleware.

Example:

app.use(express.static(‘public’));

11. What are the different types of middleware in Express.js?

• Application-level middleware

   

• Router-level middleware

   

• Error-handling middleware

   

• Built-in middleware

   

• Third-party middleware

   

12. How to get query parameters in Express.js?

Use req.query.

Example:

app.get(‘/search’, (req, res) => {

    res.send(req.query);

});

13. How to handle form data in Express.js?

Use express.urlencoded() middleware.

Example:

app.use(express.urlencoded({ extended: true }));

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

Use express.json() middleware.

app.use(express.json());

15. Explain routing parameters in Express.js?

Dynamic values in route paths.

Example:

app.get(‘/user/:id’, (req, res) => {

    res.send(req.params.id);

});

16. What is a Router in Express.js?

Router is a mini Express app that can be used to group route handlers.

Example:

const router = express.Router();

router.get(‘/’, (req, res) => res.send(‘Router Home’));

app.use(‘/api’, router);

17. How to redirect a request in Express.js?

app.get(‘/old’, (req, res) => {

    res.redirect(‘/new’);

});

18. How to set response headers in Express.js?

app.get(‘/’, (req, res) => {

    res.set(‘Content-Type’, ‘text/plain’);

    res.send(‘Hello’);

});

19. What is res.locals?

An object passed to the view engine and accessible to all templates rendered during the request.

20. How to create custom middleware in Express.js?

const logger = (req, res, next) => {

    console.log(`${req.method} ${req.url}`);

    next();

};

app.use(logger);

21. Explain express.Router() vs app?

express.Router() is isolated and modular; app is the main Express application object.

22. What is the difference between res.send(), res.json(), and res.end()?

• res.send() – sends a response (can be string, buffer, object).

   

• res.json() – sends JSON response.

   

• res.end() – ends response process without body.

   

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

Add a catch-all route at the end.

app.use((req, res) => {

    res.status(404).send(‘Not Found’);

});

24. What is the sequence of middleware execution?

In the order they are defined, unless next(‘route’) or next(err) is used.

25. How to use third-party middleware in Express.js?

Install and use them like any middleware.

Example using cors:

const cors = require(‘cors’);

app.use(cors());

Express.js continues to be a go-to framework for backend development in the Node.js ecosystem due to its flexibility, speed, and simplicity.

By going through these top Express.js interview questions and answers, you’ll be better prepared to demonstrate your skills in interviews and handle real-world project requirements.

Keep practicing, explore official documentation, and build small projects to strengthen your hands-on experience.

Bookmark this guide and revisit it as part of your interview preparation toolkit to stay ahead in your career as a Node.js or Full Stack Developer.