1. What is Node.js? 

Node.js is a runtime environment that executes JavaScript code on the server-side.

2. What is npm? 

npm (Node Package Manager) is a package manager for installing and managing Node.js packages/modules.

3. Explain the event loop in Node.js. 

The event loop is a core concept in Node.js that handles asynchronous operations by executing callbacks when events occur.

4. What is a callback function in Node.js? 

A callback function is a function passed as an argument to another function, often used for asynchronous operations.

5. What are Promises in Node.js? 

Promises are a way to handle asynchronous operations and provide a cleaner alternative to callbacks.

6. What is the purpose of the `require` function in Node.js? 

The `require` function is used to include modules in Node.js files.

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

Middleware are functions that process requests before they reach the route handlers in Express.js.

8. What is the purpose of the `next` function in Express.js middleware? 

The `next` function is used to pass control to the next middleware in the chain.

9. What is the `module.exports` object in Node.js? 

`module.exports` is used to export objects, functions, or values from a module.

10. Explain the difference between `require` and `import` in Node.js. 

`require` is used in CommonJS modules, while `import` is used in ES6 modules.

11. What is the `process` object in Node.js? 

The `process` object provides information about the Node.js process, environment variables, and more.

12. What is the purpose of the `Buffer` class in Node.js? 

The `Buffer` class is used to manipulate binary data, often used for handling streams and files.

13. What is the Event Emitter in Node.js? 

The Event Emitter is a built-in module that allows you to handle and emit events in Node.js applications.

14. How does Node.js handle concurrency? 

Node.js uses an event-driven, non-blocking I/O model to handle concurrency efficiently.

15. Explain the concept of clustering in Node.js. 

Clustering involves creating multiple instances (workers) of a Node.js process to utilize multiple CPU cores.

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

The `global` object provides access to global variables and functions across different modules.

17. What are streams in Node.js? 

Streams are objects that allow you to read or write data piece by piece, making them efficient for handling large amounts of data.

18. What is the `__dirname` and `__filename` variables in Node.js? 

`__dirname` holds the current directory name, and `__filename` holds the current file's absolute path.

19. What is the purpose of the `fs` module in Node.js? 

The `fs` module provides file system-related functionalities for reading, writing, and manipulating files.

20. Explain the role of the `path` module in Node.js. 

The `path` module is used for working with file and directory paths in a cross-platform way.

21. What is the role of the `http` module in Node.js? 

The `http` module provides functionalities to create an HTTP server and handle HTTP requests and responses.

22. Explain the concept of the `setInterval` function in Node.js. 

`setInterval` is used to repeatedly execute a function with a specified time interval.

23. What are child processes in Node.js? 

Child processes are spawned by the main Node.js process and allow you to execute external commands and scripts.

24. What is the purpose of the `os` module in Node.js? 

The `os` module provides information about the operating system, like CPU architecture and memory.

25. Explain the concept of the `crypto` module in Node.js. 

The `crypto` module is used for cryptographic functionalities, like creating secure hashes and encryption.

26. What is the significance of the `net` module in Node.js? 

The `net` module provides a way to create TCP servers and clients for network communication.

27. What is the purpose of the `url` module in Node.js? 

The `url` module provides utilities for working with URLs, like parsing and formatting.

28. Explain the concept of the `cluster` module in Node.js. 

The `cluster` module allows you to create multiple child processes that share server ports to utilize multiple cores.

29. What is the role of the `querystring` module in Node.js? 

The `querystring` module provides utilities for working with query strings in URLs.

30. What is the purpose of the `util` module in Node.js? 

The `util` module provides various utility functions for formatting and inspecting values.

31. Explain the role of the `assert` module in Node.js. 

The `assert` module provides assertion functions for testing conditions and throwing errors if they fail.

32. What are environment variables in Node.js? 

Environment variables are values set in the system environment that can be accessed by Node.js applications.

33. Explain the concept of the `zlib` module in Node.js. 

The `zlib` module provides compression and decompression functionalities for files and streams.

34. What is the purpose of the `async` module in Node.js? 

The `async` module provides utilities for handling asynchronous operations, like managing callbacks and control flow.

35. Explain the concept of the `timers` module in Node.js. 

The `timers` module provides functions to create and manage timers for executing code at specific intervals.

36. What is the role of the `dns` module in Node.js? 

The `dns` module provides functions to perform DNS (Domain Name System) lookups.

37. What is the purpose of the `os` module in Node.js? 

The `os` module provides information about the operating system, like CPU architecture and memory.

38. Explain the concept of the `readline` module in Node.js. 

The `readline` module provides an interface for reading input from readable streams, like the command line.

39. What is the role of the `util` module in Node.js? 

The `util` module provides various utility functions for formatting and inspecting values.

40. What is the purpose of the `events` module in Node.js?

The `events` module provides a way to handle and emit custom events in Node.js applications.

41. Explain the concept of the `child_process` module in Node.js. 

The `child_process` module allows you to create and manage child processes for executing external commands and scripts.

42. What is the role of the `https` module in Node.js? 

The `https` module provides functionalities to create an HTTPS server and handle HTTPS requests and responses.

43. What is the purpose of the `stream` module in Node.js? 

The `stream` module provides a way to work with streaming data, like reading and writing large files.

44. Explain the concept of the `console` object in Node.js. 

The `console` object provides methods for logging information, warnings, and errors to the console.

45. What is the role of the `assert` module in Node.js? 

The `assert` module provides assertion functions for testing conditions and throwing errors if they fail.

46. What is the purpose of the `path` module in Node.js? 

The `path` module is used for working with file and directory paths in a cross-platform way.

47. Explain the concept of the `url` module in Node.js. 

The `url` module provides utilities for working with URLs, like parsing and formatting.

48. What is the role of the `dns` module in Node.js? 

The `dns` module provides functions to perform DNS (Domain Name System) lookups.

49. What is the purpose of the `cluster` module in Node.js? 

The `cluster` module allows you to create multiple child processes that share server ports to utilize multiple cores.

50. Explain the concept of the `querystring` module in Node.js. 

The `querystring` module provides utilities for working with query strings in URLs.

51. What are the benefits of using Node.js? 

Node.js offers fast, scalable, and non-blocking I/O capabilities, making it ideal for building real-time applications and APIs.

52. Explain the concept of the CommonJS module system. 

CommonJS is a module system used in Node.js for organizing and structuring code into separate reusable modules.

53. What is the purpose of the `process.argv` property in Node.js? 

`process.argv` holds an array of command-line arguments provided to the Node.js process.

54. Explain the concept of middleware in the context of Express.js. 

Middleware functions in Express.js intercept and process HTTP requests and responses, performing tasks like authentication and logging.

55. What is a package.json file in Node.js? 

`package.json` is a metadata file that contains information about a Node.js project, including dependencies and scripts.

56. What are streams in the context of file handling in Node.js? 

Streams are used for reading or writing data in chunks, making them efficient for handling large files.

57. What is the `global` object in Node.js? 

The `global` object in Node.js contains variables and functions that are available globally across modules.

58. Explain the role of the `os` module in Node.js. 

The `os` module provides methods to retrieve information about the operating system, like CPU architecture and memory.

59. What is the purpose of the `url` module in Node.js? 

The `url` module provides utilities for parsing and formatting URLs.

60. What is the `process.nextTick()` method in Node.js? 

`process.nextTick()` schedules a function to be executed in the next iteration of the event loop.

61. What is the significance of the `path.resolve()` method in Node.js? 

`path.resolve()` converts relative paths to absolute paths and resolves any symlinks.

62. Explain the concept of the `crypto` module in Node.js. 

The `crypto` module provides cryptographic functionalities, such as generating hashes and creating digital signatures.

63. What is the purpose of the `process.env` object in Node.js? 

`process.env` provides access to environment variables, allowing configuration of application behavior.

64. What is the role of the `dns` module in Node.js? 

The `dns` module in Node.js is used for DNS (Domain Name System) lookups.

65. Explain the concept of a duplex stream in Node.js. 

A duplex stream is a type of stream that can be used for both reading and writing.

66. What is the `Buffer` class in Node.js? 

The `Buffer` class is used to handle binary data in Node.js, such as images and files.

67. What is the purpose of the `util.promisify()` function in Node.js? 

`util.promisify()` converts callback-based functions into Promise-based functions.

68. Explain the concept of the `cluster` module in Node.js. 

The `cluster` module allows you to create multiple child processes to utilize multiple CPU cores.

69. What is the purpose of the `process.cwd()` method in Node.js? 

`process.cwd()` returns the current working directory of the Node.js process.

70. What is a native addon in Node.js? 

A native addon is a dynamically linked shared library that can be loaded by Node.js modules.

71. Explain the concept of garbage collection in Node.js. 

Garbage collection is the process of automatically freeing up memory by identifying and cleaning up unused objects.

72. What is the purpose of the `util.inspect()` method in Node.js? 

`util.inspect()` is used to convert objects into human-readable strings, aiding in debugging.

73. What is the role of the `os.tmpdir()` method in Node.js? 

`os.tmpdir()` returns the operating system's default directory for temporary files.

74. Explain the concept of an EventEmitter in Node.js. 

An EventEmitter is a class in Node.js that facilitates communication between objects by emitting and handling events.

75. What is the purpose of the `stream.Readable` class in Node.js? 

The `stream.Readable` class is used for reading data from a source, such as a file or a network socket.

76. What is the Node.js `async_hooks` module used for? 

The `async_hooks` module provides a way to track asynchronous operations across different contexts.

77. Explain the concept of the `process.on()` method in Node.js. 

`process.on()` is used to register event listeners for various process-related events.

78. What is the purpose of the `util.inherits()` function in Node.js? 

`util.inherits()` is used to create inheritance relationships between constructor functions.

79. What are child processes and how are they managed in Node.js? 

Child processes are separate instances of the Node.js runtime, created using the `child_process` module, and they can be managed using features like `spawn` and `fork`.

80. Explain the concept of the `async` module in Node.js. 

The `async` module provides functions for handling asynchronous operations, simplifying control flow.

81. What is the `stream.Writable` class used for in Node.js? 

The `stream.Writable` class is used for writing data to a destination, such as a file or a network socket.

82. What is the purpose of the `util.format()` method in Node.js? 

`util.format()` is used to format strings by replacing placeholders with values.

83. Explain the concept of the `util.inspect.defaultOptions` object in Node.js. 

`util.inspect.defaultOptions` is an object that holds default options for the `util.inspect()` method.

84. What is the role of the `readline` module in Node.js? 

The `readline` module provides an interface for reading input from readable streams, particularly the command line.

85. What is the purpose of the `util.isDeepStrictEqual()` method in Node.js? 

`util.isDeepStrictEqual()` is used to compare values for deep equality, accounting for differences in objects.

86. Explain the concept of a transform stream in Node.js. 

A transform stream is a type of stream that can modify data as it passes through, making it useful for processing data during streaming.

87. What is the purpose of the `util.deprecate()` function in Node.js? 

`util.deprecate()` marks a function as deprecated, logging a warning message when it is used.

88. What is the role of the `cluster.isMaster` property in Node.js? 

`cluster.isMaster` is a boolean value that indicates whether the current process is the master process in a cluster.

89. Explain the concept of the `util.inspect.custom` symbol in Node.js. 

`util.inspect.custom` is a symbol used to customize the output of the `util.inspect()` method for user-defined objects.

90. What is the purpose of the `util.promisify.custom` symbol in Node.js? 

`util.promisify.custom` is a symbol used to customize the behavior of the `util.promisify()` function.

91. What is the role of the `module._compile()` function in Node.js? 

`module._compile()` is an internal function that compiles and executes a module's source code.

92. Explain the concept of the `os.freemem()` method in Node.js. 

`os.freemem()` returns the amount of free system memory in bytes.

93. What is the purpose of the `os.totalmem()` method in Node.js? 

`os.totalmem()` returns the total amount of system memory in bytes.

94. What is the role of the `os.arch()` method in Node.js? 

`os.arch()` returns the architecture of the operating system's CPU.

95. Explain the concept of a readable stream in Node.js. 

A readable stream is an abstraction for reading data from a source in a chunked manner.

96. What is the purpose of the `console.time()` and `console.timeEnd()` methods in Node.js? 

`console.time()` and `console.timeEnd()` are used to measure the time taken by a particular operation.

97. What is the role of the `fs.watch()` method in Node.js? 

`fs.watch()` is used to monitor changes in files and directories.

98. Explain the concept of a duplex stream in Node.js. 

A duplex stream is a type of stream that can be used for both reading and writing data.

99. What is the purpose of the `http.STATUS_CODES` object in Node.js? 

`http.STATUS_CODES` is an object that contains HTTP status codes as keys and their corresponding messages as values.

100. Explain the concept of a transform stream in Node.js. 

A transform stream is a type of stream that can modify data as it passes through, making it useful for processing data during streaming.