Top 49 Express.js Interview Questions & Answers (2026)

01 What is Express.js? 02 How do you create a basic Express.js server? 03 What is middleware in Express.js? 04 What is the difference between app.use() and app.get() in Express? 05 What are route parameters in Express.js? 06 How do you parse request bodies in Express.js? 07 What is the Express.js Router? 08 How do you send different types of responses in Express.js? 09 What is the next() function in Express middleware? 10 How does error handling work in Express.js? 11 What is CORS and how do you enable it in Express? 12 What are query parameters in Express.js? 13 How do you serve static files in Express.js? 14 What is the difference between req.params, req.query, and req.body? 15 What HTTP status codes should RESTful APIs use? 16 What is express.json() middleware? 17 What is a REST API? 18 How do you set response headers in Express.js? 19 What is the difference between app.listen() and http.createServer()? 20 What is Nodemon and why is it useful with Express?

01 How do you implement JWT authentication in Express.js? 02 What is Express middleware chaining and how does it work? 03 What is the helmet package and why should you use it? 04 How do you implement rate limiting in Express.js? 05 What is input validation and how do you do it in Express? 06 How do you connect Express.js to MongoDB using Mongoose? 07 What is async/await error handling in Express.js? 08 What is the morgan package and how is it used? 09 How do you structure a large Express.js application? 10 What is the dotenv package and how is it used in Express? 11 How do you implement pagination in an Express REST API? 12 What is express-session and how does session-based auth work? 13 How do you implement file uploads in Express.js? 14 What is compression middleware in Express and when should you use it? 15 What is the difference between PUT and PATCH in REST? 16 What is Passport.js and how does it integrate with Express? 17 How do you test an Express.js API? 18 What is Express.js Router-level middleware?

01 How do you implement WebSocket support alongside Express.js? 02 What are security best practices for Express.js APIs? 03 How does clustering work in Node.js/Express for better performance? 04 What is the difference between Express 4.x and Express 5.x? 05 How do you implement a graceful shutdown in Express.js? 06 How do you implement request tracing and correlation IDs in Express? 07 What is the Express.js application lifecycle? 08 What is the role of reverse proxies in Express.js production deployments? 09 How do you prevent SQL injection in an Express.js application? 10 What is streaming responses in Express.js and when should you use it? 11 How do you implement API versioning in Express.js?