Top 20 Express JS Interview Questions and Answers

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Express JS is a web framework for Node.js. It was created by TJ Holowaychuk in 2010 to make building web applications simpler and faster. Since then, it has become one of the most popular tools for backend development. Express helps developers handle routes, requests, and middleware with ease. If you are looking for a backend job, chances are you will be asked about Express. That’s why we have put together the top 20 most asked Express JS interview questions and answers to help prepare.

Fun Fact – According to the 2024 Stack Overflow Developer Survey, Express JS is the fifth most popular web framework and is used by 17% of developers.

Basic Level Express JS Interview Questions  

Here are some common interview questions on Express JS to help you understand the basics and get started with preparation.   

1. What is Express JS and how does it relate to Node.js?

Express JS is a web framework built on top of Node.js. It helps manage routes, requests, and responses in server-side applications. Node.js provides the runtime, while Express simplifies HTTP handling.

2. How do you create a basic Express server?

First, install Express using npm install express. Then, create a file like app.js and write:

const express = require(‘express’);

const app = express();

app.get(‘/’, (req, res) => res.send(‘Hello World’));

app.listen(3000);

3. What is the purpose of middleware in Express?

Middleware functions sit between the request and response cycle. They process requests, modify data, or handle errors before sending a response.

4. How do you handle routing in Express JS?

Routing is done using methods like app.get(), app.post(), etc. Each route takes a path and a callback to send a response.

5. What are the different types of HTTP methods supported by Express?

Express supports standard HTTP methods like –

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

6. How do you serve static files in Express?

Use express.static(). Example: app.use(express.static(‘public’)) to serve HTML, CSS, or images.

7. What is the role of app.listen() in an Express app?

It tells Express to start the server and listen on a specific port for incoming requests.

Express JS Interview Questions for Freshers 

This list of Express JS interview questions and answers is perfect for freshers looking to build a strong foundation. 

8. How do you install and set up Express in a Node.js project?

Run npm init to create a project. Then use npm install express to install Express. After that, create your app.js and write the code to define routes and start the server.

9. What does req and res mean in Express route handlers?

req is the incoming request object. It contains details like headers and data. res is the response object used to send back a reply to the client.

10. How do you define a route with route parameters in Express?

Use a colon to define a parameter: app.get(‘/user/:id’, (req, res) => { res.send(req.params.id); }).

11. What is the use of next() in middleware functions?

next() passes control to the next middleware in the stack. Without it, the request may hang.

12. How can you handle form data in an Express application?

Install and use express.urlencoded({ extended: true }) to parse form data submitted via POST.

13. What is the difference between app.get() and app.post()?

app.get() handles GET requests (usually to fetch data), while app.post() handles POST requests (usually to submit data).

14. How do you handle 404 errors in Express?

Add a middleware at the end:

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

  res.status(404).send(‘Page not found’);

});

Express JS Interview Questions Experienced 

These are advanced interview questions on Express JS for experienced professionals. 

15. How do you create and use custom middleware in Express?

You can define a function with (req, res, next) and use app.use().

Example:

function logTime(req, res, next) {

  console.log(Date.now());

  next();

}

app.use(logTime);

16. What are the pros and cons of using Express in production?

Pros: It is fast, minimal, and has a large community.

Cons: It doesn’t offer built-in security or structure, so you need to add those manually.

17. How do you manage error handling for async route handlers in Express?

Use try-catch inside async functions or wrap them with error-handling middleware. In newer setups, packages like express-async-errors help catch uncaught errors.

18. How can you organize routes using express.Router()?

Create route modules using express.Router() and import them in your main app file. It helps keep code clean in larger apps.

const router = require(‘express’).Router();

router.get(‘/users’, handler);

app.use(‘/api’, router);

19. How do you handle security concerns like CORS and HTTP headers in Express apps?

Use middleware like helmet to set security headers and cors to allow cross-origin requests safely. These packages are widely used and easy to set up.

20. How do you implement request validation in an Express project?

I usually use express-validator. It helps validate and sanitize input. 

For example:

const { body, validationResult } = require(‘express-validator’);

app.post(‘/user’, body(’email’).isEmail(), (req, res) => {

  const errors = validationResult(req);

  if (!errors.isEmpty()) return res.status(400).json(errors.array());

  res.send(‘Valid data’);

});

Tips to Prepare for Express JS Interview

Here are some practical tips to help you prepare for your upcoming Express JS interview.

• Review the official Express documentation and practice basic setups.
• Build a small CRUD app to understand routes and middleware.
• Learn how to handle errors and validate input.
• Go through real-world interview questions.
• Practice explaining concepts out loud, as you would in an interview.

Wrapping Up

These 20 Express JS interview questions and answers cover everything from basics to advanced topics. Practice them well to improve your chances of cracking backend interviews.

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Visit Hirist – an online job portal built for tech professionals. It is one of the best places to find top Express JS job openings across India.

Also Read - Top 35+ NodeJS Interview Questions and Answers

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