Top 100 Node.js interview questions and answers in 2025
Basic Interview Q&A
1. Mention the benefits of using Node.js.
Below are the main benefits of using Node.js:
- The APIs in Node.js are asynchronous which means that they do not cause blockers. This makes Node.js event-driven.
- Node.js is powered by the Google Chrome V8 JavaScript Engine, making it super fast.
- Node.js uses a single-thread model with event looping, allowing it to handle copious requests efficiently.
- There is no buffering in Node.js; data output occurs in chunks.
2. Explain global installation of dependencies.
The /npm directory stores the globally installed dependencies which can be used in the CLI of all Node.js libraries but cannot be directly imported using the require() command. Use the -g flag for global installation.
3. Explain REPL in Node.js.
REPL stands for Read Eval Print Loop. It performs tasks related to reading, executing, printing, and looping JavaScript commands interactively.
4. Define Node.js.
Node.js is a JavaScript Runtime Environment that is useful for developing server-side applications.
5. Is Node.js cross-platform?
Yes, it is compatible with Windows, Linux, Unix, and macOS.
6. What makes Node.js different?
It is different due to its asynchronous and event-driven architecture.
7. Is Node.js open-source or not?
Node.js is both open-source and cross-platform.
8. What can we build with Node.js?
Developers can build web applications, chat applications, real-time applications, streaming applications, APIs, and desktop applications.
9. Does Node.js use JavaScript?
Yes, it uses JavaScript and the V8 engine developed by Google for server-side applications.
10. Can we run Node.js on Windows?
Yes, Node.js can run on Windows.
11. What do you mean by I/O?
I/O stands for input/output, which helps in file and network operations.
12. What are the two data types categories in Node.js?
Node.js supports primitive and non-primitive data types.
13. Name types of API functions supported by Node.js.
Asynchronous non-blocking and synchronous blocking APIs are supported by Node.js.
14. Why does Google use V8 for Node.js?
Google uses V8 as it is faster and compiles JavaScript code directly into machine code.
15. Which extension is used to save Node.js files?
The .js extension is used to save Node.js files.
16. What is the full form of npm?
Npm stands for the Node package manager, used for managing dependencies in applications.
17. For what type of applications is Node.js not compatible?
Node.js is not suitable for CPU-intensive applications.
18. What is Node-Red?
Node-Red is a visual programming tool for wiring hardware devices and services as part of IoT applications.
19. How is operational error different from programming error?
An operational error is caused by application flow, while programming errors (bugs) are caused by developers.
20. What is unit testing?
Unit testing in Node.js is the process of testing individual units of code.
21. What is blocking code?
Blocking code is code that cannot execute until current code completes.
22. Are there any disadvantages of Node.js?
Node.js can face performance issues due to CPU computation blocking, and it is preferred for lightweight applications.
23. Give some examples of async functions.
Examples include setTimeout(), setInterval(), and process.nextTick().
24. Which library provides Node.js with a JavaScript engine?
The V8 library provides the JavaScript engine for Node.js.
25. How is JavaScript different from Node.js?
JavaScript is a programming language while Node.js is a runtime environment for executing JavaScript on the server-side.
26. What are some features of Node.js?
Node.js is fast, scalable, open-source, and asynchronous.
27. Can you develop network applications with Node.js?
Yes, a variety of network applications can be developed with Node.js.
28. What tasks can be done asynchronously with the help of an event loop?
Tasks like CPU computation, I/O operations, GUI programming, and database operations can be performed asynchronously.
29. What are security implementations within Node.js?
Security implementations include error handling, authentication, sanitization, encryption, and monitoring.
30. What is Package.json?
package.json defines the properties and dependencies of a Node application/module.
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36. What is the function of the fs module?
The fs module is used to create and manipulate files, providing a file system API.
37. What is the Null data type in Node.js?
It is a special data type that only takes the value null.
38. What is the difference between an event and a callback?
An event signals a change occurring, whereas a callback is a function passed to another function to execute after a certain event.
39. How will you delete a directory?
To delete a directory, use the fs.rmdir() method.
40. Explain the control flow function.
A control flow function manages the order in which code executes, allowing for asynchronous operations to be handled effectively.
41. What is an express framework?
Express is a web application framework that simplifies the development of server-side applications.
42. How does Node.js use cryptography?
Node.js implements cryptography for purposes like password hashing and securing network traffic using modules like crypto.
43. What is libuv?
Libuv is a library providing an event loop and thread pool for handling asynchronous operations.
44. How to scale a Node.js application?
Scaling can be achieved using a cluster, which allows for multiple worker processes to handle requests.
45. What is the purpose of EventEmitter?
The EventEmitter class facilitates event-driven programming by enabling the emission and listening of events in an application.