Answer:- The event loop is a mechanism in Node.js that handles asynchronous operations. It allows non-blocking I/O operations to be performed by placing them in a queue, which are then processed sequentially. It has phases such as timers, I/O callbacks, idle, and prepare, poll, check, and close callbacks.

Answer:-process.nextTick()` is used to execute a callback function immediately after the current operation completes, before the event loop continues.  – `setImmediate()` is used to schedule a callback to be executed after the current event loop cycle completes, which happens after I/O events are processed.

Answer:- `require()` is used to load modules in Node.js. It can import core modules (like `fs`, `http`), third-party modules (installed via npm), and custom modules. It caches the module after it is loaded for the first time.

Answer:- Node.js uses asynchronous file I/O operations through the `fs` module, which allows reading and writing files without blocking the event loop. Functions like `fs.readFile()` and `fs.writeFile()` are asynchronous by default, but there are also synchronous counterparts like `fs.readFileSync()`.

Answer:- Callbacks are functions passed as arguments to other functions and are executed once the task is completed. They are a common way of handling asynchronous operations in Node.js to avoid blocking the execution flow.

Answer:- Streams are objects that handle reading and writing data in chunks, allowing efficient handling of large data sets. There are four types of streams in Node.js: Readable, Writable, Duplex, and Transform.

Answer:- `Buffer`: A Buffer is a raw binary data storage object in Node.js. It is used to handle binary data streams. `String`: A String is a sequence of characters that can be manipulated easily. Buffers are often used when working with binary data, while Strings are used for textual data.

Answer:- The `cluster` module allows Node.js to take advantage of multi-core systems. It enables the creation of child processes (workers) that can share the same server port, improving performance by distributing the load across multiple CPU cores.

Answer:- Promises are objects that represent the eventual result of an asynchronous operation. They allow for chaining and provide a cleaner way to handle asynchronous code compared to callbacks. Promises have three states: pending, fulfilled, and rejected.

Answer:- `async/await` provides a way to write asynchronous code in a synchronous-like manner. `async` is used to declare a function as asynchronous, and `await` pauses the execution of code until the Promise resolves, making asynchronous code easier to read and understand.

Answer:- Exceptions in asynchronous code can be handled using `.catch()` for Promises or `try/catch` blocks when using `async/await`. Additionally, global error handling can be done using `process.on(‘uncaughtException’, callback)` for unhandled exceptions.

Answer:- The `http` module in Node.js is used to create HTTP servers and make HTTP requests. It allows you to handle HTTP requests, set response headers, and send responses.

Answer:- The `events` module in Node.js provides an EventEmitter class, which is used to handle and emit events. It allows creating custom events and listening for these events, which helps in managing asynchronous code.

Answer:- To prevent blocking the event loop, use non-blocking asynchronous operations, avoid long-running synchronous operations, and split heavy tasks into smaller chunks using techniques like `setImmediate()`, `process.nextTick()`, or by using worker threads.

Answer:- Worker threads are separate threads used to handle CPU-intensive tasks in Node.js. They are useful for parallelizing tasks to avoid blocking the event loop, improving performance in compute-heavy applications.

Answer:- Middleware in Express.js is a function that receives the request and response objects, along with the `next` function. Middleware can modify the request/response, end the request-response cycle, or call the next middleware in the stack.

Answer:- In Express.js, you can handle multiple routes by using the `.get()`, `.post()`, `.put()`, `.delete()`, etc., methods on the app object. You can define different functions for each route to handle various HTTP methods.

Answer: –Authentication in an Express application can be implemented using strategies like JWT (JSON Web Tokens), session-based authentication, or OAuth. Middleware like `passport.js` can be used to handle different authentication strategies.

Answer:- Environment variables are key-value pairs used to store configuration settings outside the application code, such as API keys, database credentials, and server configurations. They are accessed in Node.js using `process.env`.

Answer:-

`npm` is used to install and manage dependencies in Node.js projects. You can use commands like `npm install` to install packages, `npm init` to create a `package.json` file, and `npm update` to update dependencies.

Answer:- `npm` (Node Package Manager) is a package manager for JavaScript that helps in managing dependencies for Node.js projects. It allows you to install packages from the npm registry, update them, and resolve package dependencies.

Answer:- The `package.json` file is a metadata file that holds information about the project, including dependencies, scripts, version, and other configurations related to the Node.js project.

Answer:- There are three types of modules in Node.js:

1. Core modules: Built-in modules like `fs`, `http`, etc.
2. Local modules: Custom modules created by the developer.
3. Third-party modules: Modules installed via `npm`.

Answer:- `exports` is a shorthand reference to `module.exports`.   `module.exports` is the actual object that is returned when a module is `require()`d. If you assign a new object to `module.exports`, it will be returned instead of `exports`.

Answer:- In Node.js, JSON data can be handled using `JSON.parse()` to parse a JSON string into a JavaScript object and `JSON.stringify()` to convert a JavaScript object into a JSON string.

Answer:- The `path` module provides utilities for working with file and directory paths. It allows you to join, resolve, and normalize paths, making it easier to handle file system paths across different operating systems.

Answer:- `fs.watch()` is used to watch changes to a file or directory. It is an asynchronous method that notifies when a change occurs, providing the ability to monitor files and directories for updates in real-time.

Answer:- Node.js uses the V8 garbage collector to manage memory. It automatically manages memory allocation and deallocation, but developers should be mindful of memory leaks, which can occur when objects are unnecessarily retained in memory.

Answer:-  Some common process events in Node.js include:

– `exit`: Emitted when the Node.js process is about to exit.

– `uncaughtException`: Emitted when an exception is thrown but not caught by a `try/catch`.

– `SIGINT`: Emitted when the process receives a SIGINT signal (e.g., when pressing `Ctrl+C`).

Answer:-  `var`: Function-scoped variable declaration.

– `let`: Block-scoped variable declaration.

– `const`: Block-scoped variable declaration, used for constants (cannot be reassigned).

Answer:- Node.js provides advantages like:

– Non-blocking I/O.

– Scalability and high concurrency.

– A single language for both client-side and server-side (JavaScript).

– Large ecosystem of libraries and packages via `npm`.

Answer:- The `os` module provides operating system-related utility methods, like retrieving system information (hostname, architecture), memory usage, and CPU details.

Answer:- Logging in Node.js can be done using built-in methods like `console.log()`, but for more robust logging, libraries like `winston` or `bunyan` are commonly used. They provide features like log levels, file logging, and timestamping.

Answer:-

Database operations in Node.js are done using specific modules for different databases. For SQL databases, `mysql` or `pg` modules are used, and for NoSQL databases, `mongoose` for MongoDB is commonly used.

Answer:- Event-driven architecture in Node.js revolves around emitting and listening for events. The system is designed to react to events, which helps handle asynchronous processes and improve the responsiveness of applications.

Answer:-A reverse proxy is a server that forwards requests to one or more backend servers. In Node.js, reverse proxies can be set up using tools like `http-proxy-middleware` or `express-http-proxy` to route requests to backend APIs.

Answer:- The `crypto` module provides cryptographic functionality, including hash algorithms (like SHA-256), encryption, decryption, and digital signatures. It’s used for secure data handling and authentication.

Answer:- Cross-origin requests can be handled using the `cors` package in Node.js. It enables cross-origin resource sharing (CORS) by allowing the server to specify which domains are allowed to make requests to it.

Answer:- The `url` module is used to parse and manipulate URL strings. It provides methods to extract different parts of the URL, like protocol, host, path, query parameters, and more.

Answer:- Common HTTP request methods include:

– `GET`: Retrieve data from the server.

– `POST`: Send data to the server.

– `PUT`: Update data on the server.

– `DELETE`: Delete data from the server.

– `PATCH`: Partially update data on the server.

Answer:-  `app.use()`: Used to mount middleware functions on a specific route or globally.

– `app.all()`: Used to define a route that handles all HTTP methods for a specific route.

Answer:- Input validation can be implemented using libraries like `joi`, `express-validator`, or `validator`. These libraries allow validating request parameters, body data, and query strings for proper format and constraints.

Answer:- The `dns` module allows performing DNS lookups and reverse lookups. It can be used to resolve domain names into IP addresses, and vice versa.

Answer:-`stream.pipeline()` is used to compose multiple streams into a pipeline. It ensures proper error handling and manages the flow of data between streams.

Answer:- Node.js handles concurrency using an event-driven, non-blocking I/O model, allowing it to handle many requests concurrently without waiting for I/O operations to complete.

Answer:- Node.js is well-suited for microservices due to its lightweight nature, scalability, and fast I/O operations. It can handle many small, independent services that communicate over RESTful APIs or messaging queues.

Answer:- Security can be handled in Node.js through practices like input validation, preventing SQL injection, hashing passwords with `bcrypt`, using HTTPS, protecting against XSS and CSRF, and managing session security.

Answer:- `npm start` is a script defined in the `package.json` file and can execute custom commands or node applications.

– `node server.js` directly runs the `server.js` file using Node.js.

Answer:- Node.js applications can be deployed using cloud services like AWS, Google Cloud, or platforms like Heroku, using Docker containers, or on traditional VPS using a reverse proxy (e.g., Nginx).

Answer:- You can manage multiple Node.js versions using tools like `nvm` (Node Version Manager), which allows you to install, switch, and manage multiple Node.js versions on your system.