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NodeJS 200 Important Interview Questions

100 Node Js Important Interview Questions

Node.js Basics:

1. What is Node.js?
2. Explain the architecture of Node.js.
3. How does Node.js handle concurrent requests?
4. What is the role of the event loop in Node.js?
5. Describe the use of the V8 engine in Node.js.
6. How can you install a package using npm?
7. Explain the purpose of the package.json file.
8. Differentiate between process.nextTick() and setImmediate().
9. What is the purpose of the Buffer class in Node.js?
10. How can you handle environment variables in Node.js?

Modules and Dependency Management:

11. What is a module in Node.js?
12. How do you create a custom module in Node.js?
13. Explain the difference between require and import in Node.js.
14. Describe the CommonJS module system.
15. What is the purpose of the module.exports object?
16. How do you handle circular dependencies in Node.js?
17. Explain the significance of the node_modules folder.
18. What are the differences between npm install and npm ci?
19. How can you update dependencies to their latest versions using npm?
20. What is the purpose of the package-lock.json file?

Asynchronous Programming:

21. Explain the concept of callback functions in Node.js.
22. What is the Event Emitter class in Node.js, and how is it used?
23. Describe the purpose of the Promise object in Node.js.
24. How do you handle errors in asynchronous code in Node.js?
25. Compare and contrast callbacks and Promises.
26. What is the purpose of the async and await keywords in Node.js?
27. Explain the role of the setTimeout function in asynchronous programming.
28. How does Node.js handle blocking and non-blocking code?
29. Describe the use of the process.nextTick() function.

Web Development with Node.js:

30. How can you create a simple HTTP server in Node.js?
31. Explain the difference between res.send and res.end in Express.js.
32. What is middleware in Express.js?
33. How do you handle form data in an Express.js application?
34. Explain the purpose of the Express.js Router.
35. What is the purpose of the app.use function in Express.js?
36. How can you implement routing in an Express.js application?
37. Describe the role of the body-parser middleware.
38. What is RESTful API, and how can you implement it in Node.js?
39. How do you handle file uploads in an Express.js application?

Security in Node.js:

40. Explain the concept of Cross-Origin Resource Sharing (CORS).
41. How can you prevent SQL injection in a Node.js application?
42. What is the purpose of the Helmet middleware in Express.js?
43. Describe how to handle authentication in Node.js.
44. How can you protect against common security vulnerabilities in Node.js?
45. Explain the significance of the Same-Origin Policy.
46. How do you implement HTTPS in a Node.js application?
47. Describe the purpose of the crypto module in Node.js.

Testing in Node.js:

48. What is unit testing, and how can you perform it in Node.js?
49. Explain the purpose of the assert module in Node.js.
50. How do you use Mocha for testing in Node.js?
51. What is Chai, and how is it used in testing?
52. Describe the difference between unit testing and integration testing.
53. How can you mock dependencies in Node.js tests?
54. What is the purpose of the supertest library?
55. How do you test asynchronous code in Node.js?
56. Explain the significance of code coverage in testing.

Database and Data Handling:

57. How do you connect Node.js to a MongoDB database?
58. Describe the role of an Object-Relational Mapping (ORM) in Node.js.
59. What is the purpose of the sequelize library in Node.js?
60. How can you use the mongoose library for schema validation in MongoDB?
61. Explain the difference between SQL and NoSQL databases.
62. How do you perform CRUD operations in Node.js with a database?
63. Describe the purpose of connection pooling in database connections.
64. What is a transaction, and how can you implement it in Node.js?

Performance Optimization:

65. How can you improve the performance of a Node.js application?
66. Explain the purpose of the cluster module in Node.js.
67. Describe how to implement caching in a Node.js application.
68. What is the significance of the --inspect flag in Node.js?
69. How do you profile and debug a Node.js application?
70. Explain the concept of garbage collection in Node.js.

Real-time Applications:

71. How can you implement WebSockets in a Node.js application?
72. Describe the purpose of the Socket.io library.
73. How do you handle real-time updates in a Node.js application?
74. Explain the concept of server-sent events (SSE) in Node.js.
75. What is the significance of long polling in real-time applications?

Deployment and DevOps:

76. How do you deploy a Node.js application to a production server?
77. Explain the purpose of process managers like PM2 in Node.js.
78. What is Docker, and how can you use it with Node.js?
79. Describe the use of environment variables in a production Node.js application.
80. How do you monitor the performance of a deployed Node.js application?

Miscellaneous:

81. Explain the difference between process.argv and process.env in Node.js.
82. How can you use the child_process module in Node.js?
83. Describe the purpose of the os module in Node.js.
84. What is the role of the url module in Node.js?
85. How do you handle file operations in Node.js?
86. Explain the purpose of the events module in Node.js.
87. Describe the use of the fs module for file system operations.
88. How can you implement authentication using JSON Web Tokens (JWT) in Node.js?
89. What is the purpose of the stream module in Node.js?
90. How do you handle cross-platform issues in a Node.js application?

Advanced Concepts:

91. Explain the concept of microservices and how it can be implemented in Node.js.
92. How do you handle memory leaks in a long-running Node.js application?
93. Describe the purpose of the async_hooks module in Node.js.
94. How can you implement serverless architecture using Node.js?
95. Explain the concept of GraphQL and how it differs from REST.
96. How do you implement server-side rendering (SSR) in a Node.js application?
97. Describe the use of WebAssembly in Node.js.
98. How can you use the worker_threads module for multi-threading in Node.js?
99. What is the purpose of the N-API in Node.js?
100. Explain the concept of the Node.js event loop phases.