51 ExpressJS Interview Questions and Answers PDF 2025

ExpressJS helps developers create server-side code using JavaScript. Developers working with ExpressJS usually know how to handle HTTP requests, connect databases, build APIs, handle errors, and secure applications using different middleware. Knowing ExpressJS also means understanding how to create routes, manage sessions, and control user access in websites.

Preparing for an ExpressJS interview is important because it helps you answer real job questions confidently. Understanding common interview questions and answers can help you showcase your skills better during the interview. Many companies ask both technical theory and scenario based questions to check your problem solving skills.

Here, we are sharing many popular ExpressJS interview questions and answers that cover basics to advanced topics. These questions will help freshers as well as experienced developers get ready for job interviews. You’ll also find practical questions based on real-world situations.

Express.JS Interview Questions and Answers for Freshers

Lets start with basic express.js interview questions and answers:

Que 1. What is ExpressJS in Node.js?

Answer:
ExpressJS is a fast, minimal, and flexible web framework for Node.js that helps developers build APIs and web applications easily. It simplifies server-side development with built-in middleware and routing functionality.

Que 2. How do you install ExpressJS in a Node project?

Answer:
To install ExpressJS, run the following command in your terminal inside your project folder:

npm install express

Que 3. How do you create a basic ExpressJS server?

Answer:

const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.send('Hello World');
});

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

Que 4. What is middleware in ExpressJS?

Answer:
Middleware functions are functions that have access to the request and response objects. They can modify the request or response, end the request, or pass control to the next middleware function using next().

Que 5. What is the use of app.use() in ExpressJS?

Answer:
app.use() is used to apply middleware to all incoming requests. It’s helpful for tasks like logging, error handling, and parsing request bodies.

Que 6. What is routing in ExpressJS?

Answer:
Routing in ExpressJS refers to how an application responds to client requests for specific endpoints. It defines how URLs are handled.

Example:

app.get('/about', (req, res) => {
  res.send('About Page');
});

Que 7. What are HTTP methods supported by ExpressJS?

Answer:
ExpressJS supports the following HTTP methods:

• GET
• POST
• PUT
• DELETE
• PATCH
• OPTIONS
• HEAD

Que 8. How do you handle POST request data in ExpressJS?

Answer:
To handle POST request data, ExpressJS uses built-in middleware to parse JSON request bodies:

app.use(express.json());
app.post('/data', (req, res) => {
  res.send(req.body);
});

Que 9. How do you serve static files using ExpressJS?

Answer:
You can serve static files like HTML, CSS, and images using the built-in express.static middleware:

app.use(express.static('public'));

Que 10. What is next() function in ExpressJS?

Answer:
The next() function is used to pass control to the next middleware or route handler in the stack. Without calling next(), the request-response cycle will not continue.

Que 11. How do you define parameters in a route in ExpressJS?

Answer:
You can define parameters in a route using a colon : before the parameter name. For example:

app.get('/user/:id', (req, res) => {
  res.send(`User ID is ${req.params.id}`);
});

Que 12. How do you handle errors in ExpressJS?

Answer:
To handle errors, you can create a special error-handling middleware. It has four arguments: error, request, response, and next.

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

Que 13. How do you redirect a route in ExpressJS?

Answer:
You can redirect one route to another using res.redirect():

app.get('/old', (req, res) => {
  res.redirect('/new');
});

Que 14. What is the difference between app.get() and app.post() in ExpressJS?

Answer:

• app.get() is used to fetch data from the server.
• app.post() is used to send data to the server or create new data.

Que 15. How can you set headers in an ExpressJS response?

Answer:
You can set custom HTTP headers in the response using the res.set() method:

app.get('/', (req, res) => {
  res.set('Content-Type', 'text/html');
  res.send('<h1>Welcome</h1>');
});

Que 16. How to handle 404 errors in ExpressJS?

Answer:
Place a middleware at the end of all route definitions to handle 404 errors:

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

Que 17. Can you chain route handlers in ExpressJS?

Answer:
Yes, you can chain multiple middleware functions for a single route:

app.get('/example', middleware1, middleware2, (req, res) => {
  res.send('Chained response');
});

Que 18. What is the purpose of express.Router() in ExpressJS?

Answer:
express.Router() is used to create modular, mountable route handlers. It helps organize routes better in separate files.

const router = express.Router();
router.get('/test', (req, res) => res.send('Test Route'));
app.use('/api', router);

Que 19. How can you export routes from a separate file in ExpressJS?

Answer:

routes.js

const express = require('express');
const router = express.Router();
router.get('/hello', (req, res) => res.send('Hello'));
module.exports = router;

app.js

const routes = require('./routes');
app.use('/api', routes);

Que 20. What is the default port used in ExpressJS applications?

Answer:
There is no strict default port in ExpressJS. However, developers commonly use ports like 3000, 5000, or 8000 for running ExpressJS applications. You can define it using:

app.listen(3000);

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ExpressJS Interview Questions and Answers for Experienced Developers

Que 21. Explain the concept of middleware chaining in ExpressJS

Answer:
In ExpressJS, multiple middleware functions can be chained using next(). Each middleware performs a task and then calls next() to pass control to the next function in the stack. This helps build modular, reusable logic across routes.

Example:

app.use((req, res, next) => {
  console.log('Request received');
  next();
});

Que 22. How do you structure a large ExpressJS application for scalability

Answer:
Large ExpressJS applications are structured using best practices like:

• Modular route files using express.Router()
• Controller-service architecture for separating logic
• Environment-based configuration files
• Middleware folders for reusable logic
• Centralized error handling

Que 23. What is the role of body-parser and is it still required

Answer:
Earlier, body-parser was required to parse request bodies. From Express 4.16+, express.json() and express.urlencoded() are built-in and handle most use cases, reducing the need for external body-parser.

Que 24. How do you handle asynchronous errors in ExpressJS

Answer:
Async errors are handled using wrapper functions or libraries like express-async-errors.

Example:

const asyncHandler = fn => (req, res, next) => {
  Promise.resolve(fn(req, res, next)).catch(next);
};

Que 25. What is the purpose of app.locals and res.locals

Answer:

• app.locals stores variables accessible throughout the entire application.
• res.locals stores variables accessible during the life of a single request and used typically in templates.

Que 26. How can you implement rate limiting in ExpressJS

Answer:
Use the express-rate-limit package to prevent brute-force attacks and abuse.

Example:

const rateLimit = require('express-rate-limit');
app.use(rateLimit({ windowMs: 60000, max: 100 }));

Que 27. How do you secure ExpressJS apps from common web vulnerabilities

Answer:

• Use helmet to secure HTTP headers.
• Sanitize user input with express-validator or sanitize-html.
• Use HTTPS encryption.
• Prevent XSS and CSRF with proper middleware.
• Avoid exposing detailed error messages.

Que 28. What is CORS and how do you handle it in ExpressJS

Answer:
CORS (Cross-Origin Resource Sharing) controls which domains can access your API. Use the cors middleware to configure it.

Example:

const cors = require('cors');
app.use(cors({ origin: 'https://example.com' }));

Que 29. How can you log HTTP requests in ExpressJS

Answer:
Use the morgan middleware for logging HTTP requests in a structured format.

Example:

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

Que 30. How do you implement role-based access control in ExpressJS

Answer:
Create a middleware to check user roles before granting access.

Example:

function authorize(role) {
  return (req, res, next) => {
    if (req.user.role !== role) {
      return res.status(403).send('Forbidden');
    }
    next();
  };
}

Que 31. How do you organize versioned APIs in ExpressJS

Answer:
Mount different versions under unique route prefixes to manage API versions effectively.

Example:

app.use('/api/v1', require('./routes/v1'));
app.use('/api/v2', require('./routes/v2'));

Que 32. How do you write unit tests for ExpressJS routes

Answer:
Use libraries like supertest with jest or mocha for testing routes.

Example:

const request = require('supertest');
const app = require('../app');

test('GET /api/users', async () => {
  const res = await request(app).get('/api/users');
  expect(res.statusCode).toEqual(200);
});

Que 33. How do you deploy an ExpressJS app to production

Answer:

• Use PM2 for process management.
• Set NODE_ENV=production.
• Serve via a reverse proxy like Nginx.
• Enable HTTPS for secure communication.
• Optimize using compression and caching strategies.

Que 34. How do you cache API responses in ExpressJS

Answer:
Use in-memory caching like node-cache or external solutions like Redis.

Example:

const NodeCache = require('node-cache');
const cache = new NodeCache();

app.get('/data', (req, res) => {
  const cached = cache.get('key');
  if (cached) return res.send(cached);
  const result = getData();
  cache.set('key', result);
  res.send(result);
});

Que 35. How do you handle file uploads in ExpressJS

Answer:
Use the multer middleware to handle file uploads.

Example:

const multer = require('multer');
const upload = multer({ dest: 'uploads/' });

app.post('/upload', upload.single('file'), (req, res) => {
  res.send('File uploaded');
});

Que 36. How do you set up HTTPS in an ExpressJS app

Answer:
Use Node’s built-in https module to enable HTTPS.

Example:

const https = require('https');
const fs = require('fs');

const options = {
  key: fs.readFileSync('private.key'),
  cert: fs.readFileSync('certificate.crt')
};

https.createServer(options, app).listen(443);

Que 37. How can you prevent memory leaks in a long-running ExpressJS application

Answer:

• Use PM2 for monitoring and auto restarts.
• Properly close database connections.
• Avoid unnecessary global variables.
• Use tools like clinic.js or heapdump for profiling.

Que 38. What are some performance optimization techniques in ExpressJS

Answer:

• Enable gzip compression using the compression middleware.
• Cache API responses using Redis or memory caches.
• Minimize blocking synchronous code.
• Use clustering or Docker containers for load balancing.

Que 39. How do you manage environment variables in ExpressJS

Answer:
Use the dotenv package to load environment variables from a .env file.

Example:

require('dotenv').config();
const port = process.env.PORT || 3000;

Que 40. What are some popular libraries that integrate well with ExpressJS

Answer:

• mongoose or sequelize for database handling
• jsonwebtoken for authentication
• cors for CORS configuration
• helmet for securing HTTP headers
• express-validator for input validation

Top Common ExpressJS Interview Questions and Answers

These are the most common questions aksed in Express JS Interview.

Que 41. What is the purpose of express.Router() in ExpressJS

Answer:
express.Router() is used to create modular and mountable route handlers. It allows you to organize routes into separate files, improving code maintainability and scalability.

Example:

const router = express.Router();
router.get('/users', userController.getUsers);

Que 42. How do you serve static files in ExpressJS

Answer:
You can serve static files like images, CSS, and JavaScript using express.static() middleware.

Example:

app.use(express.static('public'));

This serves files from the public directory.

Que 43. How do you set up a 404 error handler in ExpressJS

Answer:
A 404 handler is created after all route definitions to handle requests that don’t match any route.

Example:

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

Que 44. How does ExpressJS handle route parameters

Answer:
Route parameters make URLs dynamic. They are accessible using req.params.

Example:

app.get('/users/:id', (req, res) => {
  res.send(`User ID: ${req.params.id}`);
});

Que 45. What are the different types of middleware in ExpressJS

Answer:
Types of middleware in ExpressJS:

• Application-level middleware (using app.use())
• Router-level middleware
• Error-handling middleware
• Built-in middleware (like express.json())
• Third-party middleware (like cors, helmet)

Que 46. How do you prevent cross-site scripting (XSS) in ExpressJS

Answer:
Prevent XSS attacks by:

• Sanitizing user input using libraries like xss-clean
• Using templating engines that auto-escape output
• Setting security headers using helmet

Que 47. What is the role of next() in ExpressJS middleware

Answer:
next() is used to pass control to the next middleware function in the request-response cycle. If next() isn’t called, the request will hang and not proceed.

Example:

function logRequest(req, res, next) {
  console.log('Request made');
  next();
}

Que 48. How can you modularize your routes in ExpressJS

Answer:
Organize routes into separate files using express.Router() to make the codebase more maintainable.

Example:

users.js

const router = require('express').Router();
router.get('/', getUsers);
module.exports = router;

Main app file

app.use('/users', require('./routes/users'));

Que 49. How do you implement global error handling in ExpressJS

Answer:
Global error handling is done using error-handling middleware with four parameters: err, req, res, and next.

Example:

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

Que 50. How do you handle JSON and URL-encoded data in ExpressJS

Answer:
ExpressJS has built-in middleware to parse incoming JSON and URL-encoded data:

app.use(express.json()); // For JSON data
app.use(express.urlencoded({ extended: true })); // For form data

This allows you to access request body data using req.body.

Que 51. How can you improve security headers in an ExpressJS application

Answer:
Use the helmet middleware to automatically set various HTTP headers that help protect your app from common vulnerabilities:

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

helmet sets headers like Content Security Policy, X-Content-Type-Options, Strict-Transport-Security, and others to secure your ExpressJS application.

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Express JS Interview Questions and Answers PDF

We have already shared 51 top ExpressJS interview questions for your preparation. To access them anytime, you can also download the PDF provided below.

FAQs: ExpressJS Interview Questions

Conclusion

We’ve provided ExpressJS interview questions and answers suitable for all experience levels, including scenario based questions. You can also download the PDF version above for easy offline access. Go through these questions to help you prepare for your next web developer interview.