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Interview Questions and Answers
1. What is the difference between a REST API and a GraphQL API, and when might you choose one over the other in a Node.js application?
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.
2. How can you improve the performance of a Node.js application?
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.
3. How do you use environment variables in Node.js?
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.
4. What is the purpose of the `module.exports` object?
`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.
5. How do you debug Node.js applications?
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).
6. What is the difference between `cluster` and `pm2` for production deployment?
`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.
7. What are middleware functions in Express.js?
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.
8. How do you handle errors in Node.js?
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.
9. Explain the difference between `require` and `import` in Node.js.
`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.
10. How do you create a basic HTTP server in Node.js?
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); });`
11. What are streams in Node.js and why are they important?
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.
12. What is Express.js and what are its benefits?
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.
13. How do you install a package using npm?
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
`.
14. What is the `package.json` file?
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.
15. What are some common Node.js frameworks and libraries?
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).
16. How does Node.js handle asynchronous operations?
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.
17. What is the event loop in Node.js?
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.
18. What are the advantages of using Node.js?
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.
19. What is 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.
20. What is Node.js?
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.