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Interview Questions and Answers

REST (Representational State Transfer) APIs expose resources as endpoints, and clients request specific data from those endpoints. GraphQL, on the other hand, allows clients to request exactly the data they need in a single query. GraphQL is often preferred when clients require fine-grained control over data retrieval and to avoid over-fetching, while REST is simpler to implement and understand for basic CRUD operations.

Several techniques can improve performance, including: caching frequently accessed data, using a process manager like PM2 for load balancing, optimizing database queries, using asynchronous operations effectively, minimizing blocking operations on the main thread, gzipping responses, and using a CDN for static assets.

You can access environment variables using `process.env`. For example, `process.env.PORT` would access the environment variable named `PORT`. Often, libraries like `dotenv` are used to load environment variables from a `.env` file during development.

`module.exports` is an object that is used to define the public interface of a Node.js module. Any properties or methods assigned to `module.exports` will be accessible from other modules that require this module.

Node.js applications can be debugged using various methods, including: using the built-in Node.js debugger (using the `node inspect` command), using Chrome DevTools by connecting to the Node.js process, using IDEs like VS Code with debugging support, and using logging statements (though this is a less efficient method for complex issues).

`cluster` is a built-in Node.js module that allows you to run multiple instances of your application on different CPU cores. `pm2` is a process manager that provides features like automatic restarts, load balancing, and monitoring. While `cluster` requires you to manage the process yourself, `pm2` offers a more comprehensive solution for managing Node.js applications in production.

Middleware functions 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 perform tasks such as logging, authentication, authorization, and request modification.

Errors in Node.js can be handled using try-catch blocks, error-first callbacks, and promises with `.catch()`. For uncaught exceptions, you can use `process.on(uncaughtException, (err) => { ... });` for logging and cleanup, but its generally recommended to avoid using this for error handling, as it can lead to unpredictable application states.

`require` is the traditional way to import modules in Node.js, using the CommonJS module system. `import` is the modern way to import modules, using the ECMAScript modules (ESM) system. To use `import`, you need to configure your project to support ESM, typically by adding `"type": "module"` to your `package.json` file.

You can create a basic HTTP server using the `http` module: `const http = require(http); const server = http.createServer((req, res) => { res.writeHead(200, { Content-Type: text/plain }); res.end(Hello, World!); }); server.listen(3000, () => { console.log(Server running on port 3000); });`

Streams are a way to handle data in chunks, allowing you to process large amounts of data efficiently without loading the entire data into memory at once. They are important for handling file uploads, video streaming, and other data-intensive operations.

Express.js is a fast, unopinionated, minimalist web framework for Node.js. Its benefits include: providing a robust set of features for web and mobile applications, making it easy to create APIs, simplifying routing, and offering a middleware system for request handling.

You can install a package using npm by running the command `npm install ` in your terminal. To install it as a development dependency, use `npm install --save-dev ` or `npm install -D `.

The `package.json` file is a JSON file that contains metadata about a Node.js project. It includes information such as the projects name, version, description, dependencies, scripts, and author. Its crucial for managing dependencies and distributing your code.

Some popular frameworks and libraries include Express.js (for building web applications and APIs), Koa.js (a more modern web framework by the same team behind Express), Socket.IO (for real-time communication), and Mongoose (for MongoDB object modeling).

Node.js uses callbacks, Promises, and async/await to handle asynchronous operations. Callbacks are functions passed as arguments to other functions, which are executed after the asynchronous operation completes. Promises are objects that represent the eventual completion (or failure) of an asynchronous operation and provide a cleaner way to handle asynchronous code than callbacks. Async/await is syntactic sugar over Promises, making asynchronous code look and behave more like synchronous code.

The event loop is a core concept in Node.js that allows it to handle non-blocking asynchronous operations. It continuously monitors the call stack and the event queue. When the call stack is empty, the event loop picks up the first event from the event queue and pushes it onto the call stack for execution.

Advantages include: fast performance due to its non-blocking architecture, scalability, a large and active community, the ability to use JavaScript on both the front-end and back-end, and a rich ecosystem of modules available through npm.

npm (Node Package Manager) is the package manager for Node.js. Its the worlds largest software registry, providing a vast collection of open-source packages that developers can use to enhance their Node.js applications.

Node.js is a runtime environment that allows you to execute JavaScript code server-side. Its built on Chromes V8 JavaScript engine and uses an event-driven, non-blocking I/O model, making it lightweight and efficient.