Interview Q&A

Short answer: An operation is idempotent if repeating it has the same effect as doing it once (e.g., PUT). Important for safe retries.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pp.get('/users', (req, res) => { res.send('Get all users'); }); pp.post('/users', (req, res) => { res.send('Create user'); }); pp.get('/users', (req, res) => { res.send('Get all users'); }); pp.post('/users', (req, res) => { res.send('Create user'); }); pp.get('/users', (req, res) => { res.send('Get all users'); }); pp.post('/users', (req, res) => {… res.send('Create user'); }); pp.get('/users', (req, res) => {…

Explain a bit more

res.send('Get all users'); }); pp.post('/users', (req, res) => { res.send('Create user'); });

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Route parameters are dynamic values in the URL, defined using :. 📌

Example code

app.get('/users/:id', (req, res) => { const id = req.params.id; res.send(`User ID: ${id}`); }); Request to /users/42 returns: User ID: 42

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use middleware like express-rate-limit to limit the number of requests per IP.

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pp.get('/users/:id', (req, res) => { const id = req.params.id; res.send(`User ID: ${id}`); }); Request to /users/42 returns: User ID: 42 pp.get('/users/:id', (req, res) => { const id = req.params.id; res.send(`User ID: ${id}`); }); Request to /users/42 returns: User ID: 42 pp.get('/users/:id', (req, res) => { const id = req.params.id; res.send(`User ID:… ${id}`); }); Request to /users/42 returns: User ID: 42…

Explain a bit more

pp.get('/users/:id', (req, res) => { const id = req.params.id; res.send(`User ID: ${id}`); }); Request to /users/42 returns: User ID: 42

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use Express’s built-in middleware: app.use(express.json()); This enables the app to read req.body in JSON POST/PUT requests.

Example code

Use Express’s built-in middleware: app.use(express.json()); This enables the app to read req.body in JSON POST/PUT requests.

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Websockets enable two-way real-time communication over a single TCP connection. Use libraries like socket.io.

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pp.use(express.json()); This enables the app to read req.body in JSON POST/PUT requests. pp.use(express.json()); This enables the app to read req.body in JSON POST/PUT requests. pp.use(express.json()); This enables the app to read req.body in JSON POST/PUT requests. pp.use(express.json()); This enables the app to read req.body in JSON POST/PUT requests.

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: CORS (Cross-Origin Resource Sharing) allows servers to specify who can access their APIs. ✅ Use the cors middleware: npm install cors const cors = require('cors'); app.use(cors()); You can also customize it: app.use(cors({ origin: ' }));

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Stateless: Each request is independent; no session stored on server. Stateful: Server keeps session info (like login status). Stateless apps scale easier. Testing & Debugging

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: PIs. ✅ Use the cors middleware: npm install cors const cors = require('cors'); pp.use(cors()); You can also customize it: pp.use(cors({ origin: ' })); PIs. ✅ Use the cors middleware: npm install cors const cors = require('cors'); pp.use(cors()); You can also customize it: pp.use(cors({ origin: ' })); PIs. ✅ Use the cors middleware: npm install cors const… cors = require('cors'); pp.use(cors()); You can also…

Explain a bit more

customize it: pp.use(cors({ origin: ' })); PIs. ✅ Use the cors middleware: npm install cors const cors = require('cors'); pp.use(cors()); You can also customize it: pp.use(cors({ origin: ' }));

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Middleware is a function that runs between the request and response cycle. It can: Modify request/response Execute logic Call the next middleware 📌

Example code

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

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use console.log for quick checks. Use node --inspect and Chrome DevTools. Use debuggers in IDEs (VSCode). Use profiling tools like clinic.js.

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pp.use((req, res, next) => { console.log(`${req.method} ${req.url}`); next(); // Move to next middleware or route }); pp.use((req, res, next) => { console.log(`${req.method} ${req.url}`); next(); // Move to next middleware or route }); pp.use((req, res, next) => { console.log(`${req.method} ${req.url}`); next(); // Move to next middleware or route });… pp.use((req, res, next) => { console.log(`${req.method}…

Explain a bit more

${req.url}`); next(); // Move to next middleware or route });

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Method Purpose app.use () Middleware for all requests app.get () Handle only GET requests 📌

Example code

app.use(authMiddleware); // Runs on all routes app.get('/data', handler); // Runs only for GET /data

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Write tests before code, then develop just enough to pass tests. Use frameworks like Mocha or Jest.

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pp.use () Middleware for all requests pp.get () Handle only GET requests 📌 pp.use(authMiddleware); // Runs on all routes pp.get('/data', handler); // Runs only for GET /data pp.use () Middleware for all requests pp.get () Handle only GET requests 📌

Example code

pp.use(authMiddleware); // Runs on all routes pp.get('/data',… handler); // Runs only for… pp.use () Middleware for all requests pp.get () Handle only GET requests 📌 Example: pp.use(authMiddleware); // Runs on all routes pp.get('/data', handler); // Runs only for GET /data pp.use () Middleware for all requests pp.get () Handle only GET requests 📌 Example: pp.use(authMiddleware); // Runs on all routes pp.get('/data',… handler); // Runs only for GET /data

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: You define a catch-all middleware after all routes: app.use((req, res) => { res.status(404).json({ message: 'Route not found' }); });

Example code

You define a catch-all middleware after all routes: app.use((req, res) => { res.status(404).json({ message: 'Route not found' }); });

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use libraries like nock to intercept and mock HTTP calls.

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pp.use((req, res) => { res.status(404).json({ message: 'Route not found' }); }); pp.use((req, res) => { res.status(404).json({ message: 'Route not found' }); }); pp.use((req, res) => { res.status(404).json({ message: 'Route not found' }); }); pp.use((req, res) => { res.status(404).json({ message: 'Route not found' }); });

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use HTTPS Implement authentication & authorization (e.g., JWT) Sanitize inputs to prevent XSS/SQLi Rate-limit requests Use helmet for HTTP headers: const helmet = require('helmet'); app.use(helmet());

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use tools like Apache JMeter, k6, or Artillery to simulate many users and measure performance. Ecosystem & Tools

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: You can use validation libraries to ensure incoming data is valid. 📌 Example with express-validator: npm install express-validator const { body, validationResult } = require('express-validator'); app.post('/users', body('email').isEmail(), (req, res) => { const errors = validationResult(req);

Example code

if (!errors.isEmpty()) return res.status(400).json({ errors: errors.array() }); res.send('User created'); });

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Node Version Manager lets you install and switch between Node.js versions easily.

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pp.post('/users', body('email').isEmail(), (req, res) => { const errors = validationResult(req); if (!errors.isEmpty()) return res.status(400).json({ errors: errors.array() }); res.send('User created'); }); pp.post('/users', body('email').isEmail(), (req, res) => { const errors = validationResult(req); if (!errors.isEmpty())… return res.status(400).json({…… errors: errors.array() }); res.send('User created'); }); pp.

Explain a bit more

post('/users', body('email').isEmail(), (req, res) => { const errors = validationResult(req); if (!errors.isEmpty()) return res.status(400).json({ errors: errors.array() }); res.send('User created'); }); pp.post('/users', body('email').isEmail(), (req, res) => { const errors = validationResult(req); if (!errors.isEmpty())… return res.status(400).json({ errors: errors.array() }); res.send('User created'); });

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.