Top 10+ Node JS Interview Questions and Answers

  • By Sarika Ganesh Kore
  • February 23, 2024
  • JavaScript
Top 10+ Node JS Interview Questions and Answers

Top 10+ Node JS Interview Questions and Answers

Prepare for success with our curated list of Top 10+ Node Js Interview Questions and Answers. 


1. What is Node.js?

Node.JS is an open-source, cross-platform JavaScript runtime environment that executes JavaScript code outside of a web browser.


2. Explain the event-driven programming in Node.js.

Node.js is designed to be event-driven, meaning that it utilizes events and callbacks to handle asynchronous operations. Events emit signals when certain actions occur, and callbacks are executed in response to these events.


3. What is npm?

npm (Node Package Manager) is the package manager for Node.js. It is used to install, manage, and share reusable JavaScript packages.


4. What is the purpose of the package.json file in Node.js projects?

The package.json file contains metadata about the Node.js project, including its dependencies, scripts, and other configuration details. It is crucial for managing the project and its dependencies.


5. Explain the difference between require and import in Node.js.

require is the common way of importing modules in Node.js, while import is part of ECMAScript modules and is used in more modern JavaScript. Node.js supports both, but using import requires using the .mjs file extension or setting the “type”: “module” in the package.json file.


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6. What is the purpose of the global object in Node.js?

The global object represents the global scope in Node.js. Variables declared in the global scope are available globally across all modules in a Node.js application.


7. Explain the concept of middleware in Express.js.

Middleware functions in Express.js have access to the request, response, and the next function in the application’s request-response cycle. They can perform tasks, modify the request or response objects, or end the request-response cycle.


8. What is the role of the package-lock.json file?

The package-lock.json file is automatically generated by npm and is used to lock down the version of each installed package in a Node.js project. It ensures that the same versions of dependencies are installed across different environments.


9. How does asynchronous programming work in Node.js?

Node.js uses an event-driven, non-blocking I/O model. It employs callbacks, Promises, and the async/await syntax to handle asynchronous operations. This allows Node.js to efficiently manage concurrent requests without blocking the execution of other code.


10. Explain the purpose of the Node.js stream module.

The stream module in Node.js provides a way of handling input and output of data in a more efficient and scalable manner. Streams allow you to read or write data in chunks, making it suitable for working with large datasets.

These questions cover a range of topics related to Node.js. Depending on the specific role and level, interview questions may vary in complexity. It’s also a good idea to be prepared to discuss your practical experience and any projects you’ve worked on using Node.js.


11. What is the purpose of the app.locals object in Express.js?

app.locals is an object that provides a way to pass data from the server to views. The data set in app.locals is available to all templates rendered by the application.


12. Explain the difference between Express.js and Node.js.

Node.js is a runtime environment for executing JavaScript outside of the browser, while Express.js is a web application framework built on top of Node.js, providing additional features and tools for building web applications.


13. How does Express.js handle routing parameters?

Express.js uses route parameters to capture values from the URL. These parameters are accessible in route handlers and can be used to create dynamic routes.


14. What is the role of the req.params object in Express.js?

req.params is an object in Express.js that contains properties mapped to the named route parameters. It allows access to values specified in the route pattern.


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15. Explain the concept of middleware chaining in Express.js.

Middleware functions in Express.js can be chained together using app.use() or specific HTTP verb methods. Middleware functions are executed sequentially in the order they are defined.


16. How does Express.js handle 404 errors?

Express.js provides a default 404 handler, which is invoked when no route matches a given request. This can be customized using middleware with a route that captures all unhandled paths.


17. What is the purpose of the Express.js Router middleware?

The Router middleware in Express.js is used to create modular, mountable route handlers. It allows you to define routes and their handlers separately and then combine them in your main application.


18. How can you handle file uploads in Express.js?

File uploads in Express.js can be handled using middleware such as multer. Multer allows you to handle multipart/form-data and supports various options for configuring file upload behavior.


19. Explain the concept of Express.js middleware sequence and execution flow.

Middleware functions in Express.js are executed in the order they are defined in the code. The execution flow continues until a middleware calls next() or the response is sent. Understanding the sequence is crucial for designing middleware logic.


20. What is Cross-Origin Resource Sharing (CORS), and how can you enable it in Express.js?

CORS is a security feature implemented by web browsers that restricts webpages from making requests to a different domain than the one that served the webpage. In Express.js, you can enable CORS using the cors middleware.


21. How can you secure an Express.js application?

Securing an Express.js application involves practices such as validating user input, using secure authentication mechanisms, implementing HTTPS, and keeping dependencies up to date. Middleware like helmet can also be used to set various HTTP headers for security.

These questions provide a deeper understanding of Express.js and cover topics that are relevant for developing robust web applications. Keep in mind that interview questions may vary based on the specific requirements of the role and the interviewer’s preferences.

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Sarika Ganesh Kore

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