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Date :- October 30, 2025  Time:-7:00 PM

✅ Backend Basics Interview Questions – Part 1 (Node.js) 🧠💻

📍 1. What is Node.js?
A: Node.js is a runtime environment that lets you run JavaScript on the server side. It uses Google’s V8 engine and is designed for building scalable network applications.

📍 2. How is Node.js different from traditional server-side platforms?
A: Unlike PHP or Java, Node.js is event-driven and non-blocking. This makes it lightweight and efficient for I/O-heavy operations like APIs and real-time apps.

📍 3. What is the role of the package.json file?
A: It stores metadata about your project (name, version, scripts) and dependencies. It’s essential for managing and sharing Node.js projects.

📍 4. What are CommonJS modules in Node.js?
A: Node uses CommonJS to handle modules. You use require() to import and module.exports to export code between files.

📍 5. What is the Event Loop in Node.js?
A: It allows Node.js to handle many connections asynchronously without blocking. It’s the heart of Node’s non-blocking architecture.

📍 6. What is middleware in Node.js (Express)?
A: Middleware functions process requests before sending a response. They can be used for logging, auth, validation, etc.

📍 7. What is the difference between process.nextTick(), setTimeout(), and setImmediate()?
A:
⦁ process.nextTick() runs after the current operation, before the next event loop.
⦁ setTimeout() runs after a minimum delay.
⦁ setImmediate() runs on the next cycle of the event loop.

📍 8. What is a callback function in Node.js?
A: A function passed as an argument to another function, executed after an async task finishes. It’s the core of async programming in Node.

📍 9. What are Streams in Node.js?
A: Streams let you read/write data piece-by-piece (chunks), great for handling large files. Types: Readable, Writable, Duplex, Transform.

📍 10. What is the difference between require and import?
A:
⦁ require is CommonJS (used in Node.js by default).
⦁ import is ES6 module syntax (used with "type": "module" in package.json).

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✅ Backend Basics Interview Questions – Part 2 (Express.js Routing) 🚀🧠

📍 1. What is Routing in Express.js?
A: Routing defines how your application responds to client requests (GET, POST, etc.) to specific endpoints (URLs).

📍 2. Basic Route Syntax

app.get('/home', (req, res) => {
  res.send('Welcome Home');
});

📍 3. Route Methods
⦁ app.get() – Read data
⦁ app.post() – Create data
⦁ app.put() – Update data
⦁ app.delete() – Delete data

📍 4. Route Parameters

app.get('/user/:id', (req, res) => {
  res.send(req.params.id);
});

📍 5. Query Parameters

app.get('/search', (req, res) => {
  res.send(req.query.keyword);
});

📍 6. Route Chaining

app.route('/product').get(getHandler).post(postHandler).put(putHandler);

📍 7. Router Middleware

const router = express.Router();
router.get('/about', (req, res) => res.send('About Page'));
app.use('/info', router);  // URL: /info/about

📍 8. Error Handling Route

app.use((req, res) => {
  res.status(404).send('Page Not Found');
});

💡 Pro Tip: Always place dynamic routes after static ones to avoid conflicts.

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✅ Backend Basics Interview Questions – Part 3 (Express.js Middleware) 🚀🧠

📍 1. What is Middleware in Express.js?
A: Middleware are functions that execute during the request-response cycle. They can modify req/res, execute code, or end the request.

📍 2. Types of Middleware
⦁ Application-level: Applied to all routes or specific routes (using app.use())
⦁ Router-level: Applied to router instances
⦁ Built-in: e.g., express.json(), express.static()
⦁ Third-party: e.g., cors, morgan, helmet

📍 3. Example – Logging Middleware

app.use((req, res, next) => {
  console.log(`${req.method} ${req.url}`);
  next(); // Pass to next middleware/route
});

📍 4. Built-in Middleware

app.use(express.json()); // Parses JSON body
app.use(express.urlencoded({ extended: true })); // Parses URL-encoded body
app.use(express.static('public')); // Serves static files

📍 5. Router-level Middleware

const router = express.Router();
router.use((req, res, next) => {
  console.log('Router Middleware Active');
  next();
});
app.use('/api', router);

📍 6. Error-handling Middleware

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

📍 7. Chaining Middleware

app.get('/profile', authMiddleware, logMiddleware, (req, res) => {
  res.send('User Profile');
});

💡 Pro Tip: Middleware order matters—always place error-handling middleware last.

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✅ Backend Basics Interview Questions – Part 4 (REST API) 🚀💻

📍 1. What is a REST API?
A: REST (Representational State Transfer) APIs allow clients to interact with server resources using HTTP methods like GET, POST, PUT, DELETE.

📍 2. Difference Between REST & SOAP
⦁ REST is an architectural style using HTTP, lightweight, and supports JSON/XML for stateless communication.
⦁ SOAP is a strict protocol, heavier, XML-only, stateful, with built-in standards for enterprise reliability and security.

📍 3. HTTP Methods
⦁ GET → Read data
⦁ POST → Create data
⦁ PUT → Update data (full replacement)
⦁ DELETE → Delete data
⦁ PATCH → Partial update

📍 4. Example – Creating a GET Route

app.get('/users', (req, res) => {
  res.send(users); // Return all users
});

📍 5. Example – POST Route

app.post('/users', (req, res) => {
  const newUser = req.body;
  users.push(newUser);
  res.status(201).send(newUser);
});

📍 6. Route Parameters & Query Parameters

app.get('/users/:id', (req, res) => {
  res.send(users.find(u => u.id == req.params.id));
});
app.get('/search', (req, res) => {
  res.send(users.filter(u => u.name.includes(req.query.name)));
});

📍 7. Status Codes
⦁ 200 → OK
⦁ 201 → Created
⦁ 400 → Bad Request
⦁ 404 → Not Found
⦁ 500 → Server Error

📍 8. Best Practices
⦁ Validate request data
⦁ Handle errors properly
⦁ Use consistent endpoint naming (e.g., /api/v1/users)
⦁ Keep routes modular using express.Router()

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