Top 40+ Nodejs Interview Question and Answer for Programmer | Nodejs Question |

1. What is Node.js?

• Node.js is an open-source, server-side runtime environment built on Chrome’s V8 JavaScript engine. It allows you to execute JavaScript code on the server-side.

1. Explain event-driven programming in Node.js.

• Node.js is based on an event-driven architecture where certain events trigger the execution of functions. These events could be I/O operations, network requests, or timers.

1. What is NPM?

• NPM (Node Package Manager) is the default package manager for Node.js. It is used to install, share, and manage packages or modules of JavaScript code written for Node.js.

1. What is a module in Node.js?

• A module in Node.js is a reusable block of code whose behavior can be shared throughout a Node.js application. It can be a single file or a directory containing multiple files.

1. What is the difference between require() and import in Node.js?

• require() is a CommonJS module system method used to import modules in Node.js, while import is an ECMAScript (ES6) feature used for the same purpose. import is generally preferred for ES6 modules, but it requires using a transpiler like Babel in Node.js.

1. How can you handle asynchronous operations in Node.js?

• Asynchronous operations in Node.js can be handled using callbacks, promises, or async/await syntax.

1. What are callbacks in Node.js?

• Callbacks are functions passed as arguments to other functions in Node.js. They are invoked once the asynchronous operation is completed or an error occurs.

1. Explain the purpose of process.argv in Node.js.

• process.argv is an array containing command-line arguments passed to the Node.js process. The first element is the path to the Node.js executable, the second element is the path to the script file being executed, and the subsequent elements are the command-line arguments.

1. What is the difference between process.nextTick() and setImmediate()?

• process.nextTick() queues a function to be executed at the beginning of the next event loop iteration, while setImmediate() queues a function to be executed at the end of the current event loop iteration.

1. Explain the role of the Buffer class in Node.js.
   • The Buffer class in Node.js is used to handle binary data. It provides methods for encoding and decoding binary data, and it is particularly useful for working with streams and file system operations.
2. What is the purpose of the util module in Node.js?
   • The util module in Node.js provides utility functions that are helpful for debugging, error handling, and working with objects in JavaScript.
3. How can you handle errors in Node.js?
   • Errors in Node.js can be handled using try-catch blocks for synchronous code and by passing error-first callbacks or using promises for asynchronous code.
4. Explain the purpose of the __dirname and __filename variables in Node.js.
   • __dirname is a global variable that stores the directory name of the current module, while __filename is a global variable that stores the file name of the current module.
5. What is middleware in Express.js?
   • Middleware in Express.js are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. They can modify the request and response objects, end the request-response cycle, or call the next middleware function.
6. What is the purpose of the body-parser middleware in Express.js?
   • The body-parser middleware in Express.js is used to parse the body of incoming HTTP requests. It can parse various types of request bodies, such as JSON, URL-encoded, and multipart.
7. Explain the difference between app.get() and app.use() in Express.js.
   • app.get() is a method used to define a route that matches the GET HTTP method, while app.use() is a method used to mount middleware functions at a specified path. app.get() is used for route-specific middleware, while app.use() is used for application-wide middleware.
8. What is JWT authentication and how is it implemented in Node.js?
   • JWT (JSON Web Token) authentication is a method of authenticating users in web applications using tokens. In Node.js, JWT authentication involves generating a token containing user information upon successful login and including this token in subsequent requests for authorization.
9. Explain the purpose of the cluster module in Node.js.
   • The cluster module in Node.js is used to spawn child processes that share server ports. It allows you to take advantage of multi-core systems by creating a cluster of Node.js processes to handle incoming HTTP requests.
10. What is the purpose of the child_process module in Node.js?
    • The child_process module in Node.js is used to create child processes. It provides methods for spawning new processes, communicating with them via stdin/stdout/stderr streams, and controlling their lifecycle.
11. How can you improve the performance of a Node.js application?
    • Performance of a Node.js application can be improved by optimizing code, caching data, using clustering to take advantage of multi-core systems, minimizing blocking I/O operations, and using efficient algorithms and data structures.

Certainly! Here are some more Node.js related questions along with their answers:

21. What is the event loop in Node.js?
    • The event loop is the core mechanism of Node.js that allows it to perform non-blocking I/O operations asynchronously. It continuously checks the event queue for pending events and executes them one by one in a loop.
22. Explain the concept of non-blocking I/O in Node.js.
    • Non-blocking I/O means that Node.js can perform I/O operations (such as reading from files or making network requests) without waiting for the operation to complete. Instead, it delegates the operation to the operating system and continues executing other code. When the operation completes, a callback function is invoked to handle the result.
23. What are streams in Node.js?
    • Streams in Node.js are objects that allow you to read data from a source or write data to a destination in a continuous manner. They are used to handle large amounts of data efficiently, without loading the entire dataset into memory.
24. What are the different types of streams in Node.js?
    • Node.js provides four types of streams: Readable, Writable, Duplex, and Transform. Readable streams are used for reading data, Writable streams are used for writing data, Duplex streams can be used for both reading and writing, and Transform streams are a type of Duplex stream that allows data to be modified as it is being read or written.
25. Explain the difference between synchronous and asynchronous code execution in Node.js.
    • Synchronous code execution means that each statement in the code is executed one after the other, blocking the execution of subsequent code until the current statement completes. Asynchronous code execution, on the other hand, allows multiple operations to be performed concurrently, with callback functions being invoked when each operation completes.
26. What is the purpose of the fs module in Node.js?
    • The fs module in Node.js provides functions for interacting with the file system. It allows you to perform operations such as reading from and writing to files, creating directories, and querying file metadata.
27. Explain the purpose of the http module in Node.js.
    • The http module in Node.js is used to create HTTP servers and make HTTP requests. It provides classes and functions for handling incoming HTTP requests, sending HTTP responses, and creating HTTP clients.
28. What is middleware in the context of Express.js?
    • Middleware in Express.js are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. They can be used to perform tasks such as logging, authentication, and error handling.
29. How can you handle file uploads in Node.js?
    • File uploads in Node.js can be handled using the multer middleware in combination with Express.js. multer allows you to parse multipart/form-data, which is commonly used for file uploads in HTML forms.
30. What is the purpose of the path module in Node.js?
    • The path module in Node.js provides utilities for working with file and directory paths. It allows you to manipulate file paths in a platform-independent manner, handling differences in path separators and resolving relative