Q1: What is Node.js?
Node.js is an open-source, server-side JavaScript runtime environment that allows developers to build scalable and high-performance applications. It uses an event-driven, non-blocking I/O model which makes it lightweight and efficient for handling concurrent requests.

Q2: What are the main features of Node.js?
The main features of Node.js are:
1. Asynchronous and event-driven programming model.
2. Highly scalable and efficient for handling concurrent requests.
3. Single-threaded, but can support multiple concurrent connections.
4. Built-in support for package management through npm (Node Package Manager).
5. Easy integration with various web servers.
6. Ability to run JavaScript on both the server and client side.

Q3: What is npm?
npm (Node Package Manager) is a default package manager for Node.js. It is a command-line tool that allows developers to install, publish, and manage third-party packages/modules. npm also provides a platform for developers to share their own packages with the community.

Q4: How can you read data from a file in Node.js?
To read data from a file in Node.js, you can use the built-in fs module. Here’s an example:

“`javascript
const fs = require(‘fs’);
fs.readFile(‘filename.txt’, ‘utf8’, (err, data) => {
if (err) throw err;
console.log(data);
});
“`

Q5: What is the purpose of the ‘require’ keyword in Node.js?
The ‘require’ keyword is used in Node.js to import modules. It allows you to include external libraries or modules into your application.

Q6: What are streams in Node.js?
Streams in Node.js are objects used to handle continuous data flow. They can be used to read data from a source, write data to a destination, or both. There are several types of streams, such as Readable, Writable, and Duplex.

Q7: How can you create a simple HTTP server in Node.js?
To create a simple HTTP server in Node.js, you can use the built-in ‘http’ module. Here’s an example:

“`javascript
const http = require(‘http’);
const server = http.createServer((req, res) => {
res.statusCode = 200;
res.setHeader(‘Content-Type’, ‘text/plain’);
res.end(‘Hello, World!’);
});
server.listen(3000, ‘localhost’, () => {
console.log(‘Server running at http://localhost:3000/’);
});
“`

Q8: What is the purpose of the ‘process’ object in Node.js?
The ‘process’ object in Node.js provides information and control over the current Node.js process. It can be used to get environment variables, exit the process, listen for signals, etc.

Q9: What is the difference between ‘forEach’ and ‘map’ methods in JavaScript?
‘forEach’ and ‘map’ are both array methods in JavaScript. The main difference is that ‘forEach’ is used to iterate over an array and execute a provided function for each element, whereas ‘map’ creates a new array by applying a provided function to each element of the original array.

Q10: How can you handle errors in Node.js?
In Node.js, errors can be handled using try-catch blocks or by using the error-first callback pattern. The error-first callback pattern involves passing an error object as the first argument to a callback function, indicating whether an error occurred or not.

Q11: What is middleware in Node.js?
Middleware is a function or set of functions that can be executed before or after the main request handler in an HTTP server. It is commonly used for tasks such as logging, authentication, and error handling.

Q12: What is the difference between ‘require’ and ‘import’ in Node.js?
‘require’ is a CommonJS module system syntax used in Node.js, while ‘import’ is an ES6 module system syntax used in modern JavaScript. ‘require’ is used to import modules in Node.js, whereas ‘import’ is used in JavaScript running on the client-side.

Q13: What is an EventEmitter in Node.js?
An EventEmitter is a class in Node.js that allows us to create and handle custom events. It is a central communication channel between different parts of a Node.js application.

Q14: What is the purpose of the global object in Node.js?
The global object in Node.js provides global variables and functions that are available throughout the application. It allows you to define variables or functions that can be accessed from any module without the need for importing.

Q15: How can you update Node.js to the latest version?
To update Node.js to the latest version, you can use the npm package manager. Open your command-line interface and run the following two commands:
1. npm install -g n (to install the n package)
2. n latest (to update Node.js to the latest version)

Q16: What is event loop in Node.js?
The event loop in Node.js is a mechanism that allows the Node.js runtime to handle multiple events asynchronously. It is responsible for managing callback queues, executing callbacks, and handling I/O operations efficiently.

Q17: How can you create a child process in Node.js?
In Node.js, you can create child processes using the built-in ‘child_process’ module. It provides methods to spawn child processes, execute commands, and communicate with the parent process.

Q18: What is the purpose of the ‘module’ object in Node.js?
The ‘module’ object in Node.js represents the current module and provides access to the module’s properties and functions. It is available in every module and can be used to export and import functions or variables.

Q19: What is the use of ‘cluster’ module in Node.js?
The ‘cluster’ module in Node.js allows you to create a cluster of child processes to distribute the workload across multiple CPU cores. It improves the performance and scalability of Node.js applications.

Q20: How can you handle file uploads in Node.js?
To handle file uploads in Node.js, you can use the ‘multer’ middleware package. It simplifies the process of handling multipart/form-data requests and storing uploaded files on the server.

1. What is Node.js?
Node.js is a runtime environment that allows developers to run JavaScript code on the server-side. It uses an event-driven, non-blocking I/O model to handle concurrent requests efficiently.

2. What are streams in Node.js?
Streams are objects used to handle reading and writing data in Node.js. They provide an efficient way to handle large amounts of data without loading them into memory completely.

3. How does Node.js handle child processes?
Node.js allows the execution of external commands or shell scripts as child processes using the `child_process` module. It provides methods like `spawn`, `exec`, and `fork` to handle different use cases.

4. What is the purpose of the `cluster` module in Node.js?
The `cluster` module in Node.js allows the creation of child processes that share server ports to handle multiple requests concurrently. It helps in scaling Node.js applications across multiple CPU cores.

5. What is the purpose of the `global` object in Node.js?
The `global` object in Node.js represents the global scope, similar to the `window` object in browsers. It provides a way to define global variables and functions that are accessible throughout the application.

6. How can you handle uncaught exceptions in Node.js?
Node.js provides a way to handle uncaught exceptions using the `process.on(‘uncaughtException’)` event. By listening to this event, you can perform cleanup tasks and gracefully exit the application.

7. Explain the concept of Middleware in Express.js.
Middleware functions in Express.js are functions that have access to the request and response objects. They can perform operations on the request or response and pass control to the next middleware function in the chain.

8. How can you handle file uploads in Node.js?
File uploads in Node.js can be handled using middleware like `multer`. Multer is a middleware that adds support for handling multipart/form-data, which is commonly used for file uploads.

9. What is Event-driven programming in Node.js?
Event-driven programming in Node.js is a programming paradigm where the flow of the program is determined by events. Events are emitted by objects, and the program responds to these events by executing callback functions.

10. How can you handle memory leaks in a Node.js application?
To handle memory leaks in a Node.js application, you can use tools like the built-in `heapdump` module, which captures and analyzes memory snapshots. You can also use memory profiling tools like `node-memwatch` to detect and fix leaks.

11. How does Node.js handle modules?
Node.js uses the CommonJS module system to handle modules. Each file in Node.js is treated as a separate module, and modules can export functions, objects, or variables to be used by other modules using the `module.exports` object.

12. How can you handle large file uploads in Node.js?
To handle large file uploads in Node.js, you can use a streaming approach. Instead of buffering the entire file in memory, you can read and process chunks of data one at a time, using the `fs` and `stream` modules.

13. How can you improve the performance of a Node.js application?
To improve the performance of a Node.js application, you can use techniques like code optimization, caching, load balancing, using a CDN, and optimizing database queries. Additionally, you can use clustering to make use of multiple CPU cores.

14. Explain the concept of garbage collection in Node.js.
Garbage collection in Node.js is a process where the JavaScript runtime automatically frees up memory by removing objects that are no longer in use. Node.js uses the V8 JavaScript engine, which has a garbage collector built-in.

15. How can you handle authentication and authorization in Node.js?
Authentication and authorization can be handled in Node.js using libraries like Passport.js or by implementing custom middleware. These libraries provide strategies for authentication with various providers such as OAuth, JWT, and local username/password authentication.

16. What is the purpose of the `util` module in Node.js?
The `util` module in Node.js provides various utility functions that can be used for debugging, error handling, object inspection, and other common tasks. It provides functions like `util.promisify`, `util.inspect`, and `util.format`.

17. How can you handle HTTPS requests in Node.js?
Node.js provides a `https` module that can be used to handle HTTPS requests. You can create an HTTPS server using the `https.createServer` method and handle requests in a similar way as with an HTTP server.

18. 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 provides methods like `path.resolve`, `path.join`, and `path.basename` to manipulate paths and perform operations on them.

19. How can you handle errors in asynchronous Node.js code?
To handle errors in asynchronous Node.js code, you can use the `try…catch` block or attach an error callback using the Promise-based `catch` method. Additionally, you can use the `unhandledRejection` event to handle unhandled promise rejections.

20. How can you test Node.js applications?
Node.js applications can be tested using testing frameworks like Mocha, Jest, or Jasmine. These frameworks allow you to write test cases, run them, and perform assertions to ensure the correctness of your code.