58 Must-Know Express.js Interview Questions and Answers 2024

Express.js Fundamentals

1.
What is Express.js, and how does it relate to Node.js?
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2.
Explain the concept of middleware in Express.js.
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3.
How would you set up a basic Express.js application?
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4.
What is the purpose of the app.use() function?
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5.
How do you serve static files using Express.js?
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6.
Discuss the difference between app.get() and app.post() in Express.js.
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7.
How do you retrieve the URL parameters from a GET request in Express.js?
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8.
What are route handlers, and how would you implement them?
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9.
How do you enable CORS in an Express.js application?
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10.
Explain the use of next() in Express.js middleware.
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Routing and Requests

11.
What is the role of the express.Router class?
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12.
How do you handle 404 errors in Express.js?
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13.
What are the differences between req.query and req.params?
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14.
Describe the purpose of req.body and how you would access it.
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15.
How do you create a middleware that logs the request method and URL for every request?
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16.
Explain how you would implement nested routes in Express.js.
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17.
How can you capture and respond to URL parameters in a route?
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18.
How do you serve different content types (e.g., JSON, HTML) with Express.js responses?
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19.
What are best practices for structuring a large Express.js application with multiple routes?
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Middleware and Error Handling

20.
Explain the concept and use of built-in middleware in Express.js.
Answer:
21.
How do you write custom middleware functions in Express.js?
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22.
How do you handle file uploads in Express.js?
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23.
What is express-session, and how would you use it?
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24.
Discuss error handling in an Express.js application. How do you define an error-handling middleware?
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25.
Provide an example of using third-party middleware, such as body-parser or morgan.
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26.
How do you protect against SQL injection or other security threats in Express.js?
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Response and Performance

27.
How would you implement caching in an Express.js application?
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28.
How do you set cookies and get cookies in an Express.js application?
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29.
What are ways to improve the performance of Express.js applications?
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30.
How do you configure an Express.js app for a reverse proxy, like Nginx?
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31.
Explain the purpose of template engines. How would you integrate one with Express.js?
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Testing and Debugging

32.
How do you test an Express.js application?
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33.
Discuss common debugging techniques for Express.js applications.
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34.
What is the role of environment variables in an Express.js application?
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35.
How do you use a debugger with an Express.js app running in Node.js?
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Express.js with Databases

36.
How would you connect a MongoDB database with an Express.js application?
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37.
Explain how to integrate an ORM like Sequelize with Express.js.
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38.
How do you handle database errors in Express.js?
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39.
What are the advantages of using a database pooling mechanism in an Express.js app?
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Authentication and Authorization

40.
Describe how you would implement user authentication in Express.js.
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41.
Explain how sessions are managed in Express.js.
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42.
Discuss how you would handle user roles and permissions in an Express.js application.
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43.
How can you secure passwords and sensitive information in your Express.js app?
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Integration and Configuration

44.
How do you integrate a third-party API in an Express.js application?
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45.
Explain the steps to deploy an Express.js application to a cloud provider like AWS or Heroku.
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46.
How can you ensure that your Express.js application is scalable_?
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47.
What is the Twelve-Factor App methodology, and how does it apply to Express.js?
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Coding Challenges

48.
Write an Express.js middleware function that limits requests to 100 per hour per IP address.
Answer:
49.
Create an Express.js route that accepts a JSON payload and responds with the same payload in reverse order.
Answer:
50.
Develop a simple REST API with Express.js that includes CRUD operations for managing books. Include route definitions and handler functions that interact with a placeholder data store.
Answer:

Advanced Topics and Best Practices

51.
Discuss strategies for building a real-time application with Express.js.
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52.
What are some common optimization techniques for Express.js applications?
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53.
Explain the concept and benefits of server-side rendering with Express.js and a templating engine.
Answer:
54.
How do you ensure that your Express.js code is maintainable and follows best practices?
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Case Studies and Scenario-Based Questions

55.
How would you structure an Express.js application for a large-scale e-commerce platform?
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56.
Describe the key considerations for building a secure API with Express.js.
Answer:
57.
Discuss how to handle session management in a distributed Express.js application.
Answer:
58.
What are the implications of microservices architecture for an Express.js application?
Answer:

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58 Express.js interview questions

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

Explain the concept of middleware in Express.js.

How would you set up a basic Express.js application?

What is the purpose of the app.use() function?

How do you serve static files using Express.js?

Discuss the difference between app.get() and app.post() in Express.js.

How do you retrieve the URL parameters from a GET request in Express.js?

What are route handlers, and how would you implement them?

How do you enable CORS in an Express.js application?

Explain the use of next() in Express.js middleware.

What is the role of the express.Router class?

How do you handle 404 errors in Express.js?

What are the differences between req.query and req.params?

Describe the purpose of req.body and how you would access it.

How do you create a middleware that logs the request method and URL for every request?

Explain how you would implement nested routes in Express.js.

How can you capture and respond to URL parameters in a route?

How do you serve different content types (e.g., JSON, HTML) with Express.js responses?

What are best practices for structuring a large Express.js application with multiple routes?

Explain the concept and use of built-in middleware in Express.js.

How do you write custom middleware functions in Express.js?

How do you handle file uploads in Express.js?

What is express-session, and how would you use it?

Discuss error handling in an Express.js application. How do you define an error-handling middleware?

Provide an example of using third-party middleware, such as body-parser or morgan.

How do you protect against SQL injection or other security threats in Express.js?

How would you implement caching in an Express.js application?

How do you set cookies and get cookies in an Express.js application?

What are ways to improve the performance of Express.js applications?

How do you configure an Express.js app for a reverse proxy, like Nginx?

Explain the purpose of template engines. How would you integrate one with Express.js?

How do you test an Express.js application?

Discuss common debugging techniques for Express.js applications.

What is the role of environment variables in an Express.js application?

How do you use a debugger with an Express.js app running in Node.js?

How would you connect a MongoDB database with an Express.js application?

Explain how to integrate an ORM like Sequelize with Express.js.

How do you handle database errors in Express.js?

What are the advantages of using a database pooling mechanism in an Express.js app?

Describe how you would implement user authentication in Express.js.

Explain how sessions are managed in Express.js.

Discuss how you would handle user roles and permissions in an Express.js application.

How can you secure passwords and sensitive information in your Express.js app?

How do you integrate a third-party API in an Express.js application?

Explain the steps to deploy an Express.js application to a cloud provider like AWS or Heroku.

How can you ensure that your Express.js application is scalable_?

What is the Twelve-Factor App methodology, and how does it apply to Express.js?

Write an Express.js middleware function that limits requests to 100 per hour per IP address.

Create an Express.js route that accepts a JSON payload and responds with the same payload in reverse order.

Develop a simple REST API with Express.js that includes CRUD operations for managing books. Include route definitions and handler functions that interact with a placeholder data store.

Discuss strategies for building a real-time application with Express.js.

What are some common optimization techniques for Express.js applications?

Explain the concept and benefits of server-side rendering with Express.js and a templating engine.

How do you ensure that your Express.js code is maintainable and follows best practices?

How would you structure an Express.js application for a large-scale e-commerce platform?

Describe the key considerations for building a secure API with Express.js.

Discuss how to handle session management in a distributed Express.js application.

What are the implications of microservices architecture for an Express.js application?

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What is the purpose of the `app.use()` function?

Discuss the difference between `app.get()` and `app.post()` in Express.js.

Explain the use of `next()` in Express.js middleware.

What is the role of the `express.Router` class?

What are the differences between `req.query` and `req.params`?

Describe the purpose of `req.body` and how you would access it.

What is `express-session`, and how would you use it?

Provide an example of using third-party middleware, such as `body-parser` or `morgan`.