Interview Q&A

Short answer: Avoid blocking the event loop. Use asynchronous APIs. Use clustering or worker threads. Cache results where possible. Profile and fix bottlenecks. Use load balancers for scaling horizontally.

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: const EventEmitter = require('events'); const emitter = new EventEmitter(); emitter.on('greet', (name) => { console.log(`Hello, ${name}!`); }); emitter.emit('greet', 'Alice'); // Output: Hello, Alice!

Example code

const EventEmitter = require('events');
const emitter = new EventEmitter(); emitter.on('greet', (name) => { console.log(`Hello, ${name}!`); }); emitter.emit('greet', 'Alice'); // Output: Hello, Alice!

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: Local Installation (default): Installs the package into the node_modules folder of your current project. npm install lodash ✅ Used when the package is needed as part of your app's code. Global Installation: Installs the package system-wide, making it available in the command line anywhere. npm install -g nodemon ✅ Used for tools/CLI apps like nodemon, eslint, typescript, etc.

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: Clustering runs multiple Node.js instances on different CPU cores sharing the same server port. This spreads load and uses full CPU capacity, increasing concurrency.

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.js uses a single-threaded event loop to handle many I/O operations asynchronously, allowing it to handle thousands of concurrent connections efficiently without creating threads per connection.

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: Deploy multiple instances on different machines or containers. Use a load balancer to distribute traffic. Share state externally (e.g., Redis) since instances are stateless.

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: llowing it to handle thousands of concurrent connections efficiently without creating threads per connection.

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: Global variables holding references. Event listeners not removed. Closures holding onto variables. Caches growing without limits. Security & Best Practices

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: To update all packages to their latest safe versions based on semver: npm update To update a specific package to its latest version: npm install express@latest For a more interactive way: npx npm-check-updates -u npm install ✅ The npm-check-updates tool helps update versions in your package.json.

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 create a custom module by writing logic in a separate .js file and exporting it using module.exports.

Explain a bit more

📌 Example: mathUtils.js function add(a, b) { return a + b; module.exports = { add, subtract }; app.js const math = require('./mathUtils'); console.log(math.add(5, 3)); // 8 console.log(math.subtract(9, 4)); // 5 ✅ This is how you break your code into reusable pieces (modules) in Node.js. REST API Development in Node.js

Example code

} function subtract(a, b) { return a - b;
}

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: Use rate limiting. Validate and sanitize inputs. Avoid blocking event loop. Use security middleware like helmet. Use a reverse proxy with DDoS protection.

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.js const math = require('./mathUtils'); console.log(math.add(5, 3)); // 8 console.log(math.subtract(9, 4)); // 5 ✅ This is how you break your code into reusable pieces (modules) in Node.js. REST API Development in Node.js pp.js const math = require('./mathUtils'); console.log(math.add(5, 3)); // 8 console.log(math.subtract(9, 4)); // 5 ✅ This is how you break your code into reusable pieces (modules) in Node.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: Strip out dangerous characters. Use libraries like validator.js. Escape output in HTML contexts.

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: RESTful APIs use the following standard HTTP methods: Method Purpose GET Retrieve data POST Create new data PUT Update existing PATCH Partial update DELETE Remove 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: Cross-Origin Resource Sharing controls which domains can access your API. Configure with the cors package: const cors = require('cors'); 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: Name commonly used ones. HTTP status codes indicate the result of a request: Code Meaning 200 OK 201 Created 400 Bad Request 401 Unauthorized 403 Forbidden 404 Not Found 500 Internal Server Error 📌

Example code

res.status(201).json({ message: 'User created successfully' });

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(cors({ origin: ' })); pp.use(cors({ origin: ' })); pp.use(cors({ origin: ' })); pp.use(cors({ origin: ' })); pp.use(cors({ origin: ' })); pp.use(cors({ origin: ' })); pp.use(cors({ origin: ' })); 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: HTTP status codes indicate the result of a request: Code Meaning 200 OK 201 Created 400 Bad Request 401 Unauthorized 403 Forbidden 404 Not Found 500 Internal Server Error 📌 res.status(201).json({ message: 'User created successfully' }); HTTP status codes indicate the result of a request: Code Meaning 200 OK 201 Created… 400 Bad Request 401… Unauthorized 403 Forbidden 404 Not Found 500 Internal Server Error 📌

Example code

res.status(201).json({ message: 'User created successfully' }); HTTP status codes indicate the result of a request: Code Meaning 200 OK 201 Created 400 Bad Request 401 Unauthorized 403 Forbidden 404 Not Found 500 Internal Server Error 📌 Example: res.status(201).json({ message: 'User created successfully' }); HTTP status codes indicate the result of a request: Code Meaning 200 OK 201 Created… 400 Bad Request 401 Unauthorized 403 Forbidden 404 Not Found 500 Internal Server Error 📌 Example: res.status(201).json({ message: 'User created successfully' });

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: Using Express.js, you can quickly set up routes and logic. 📌 Example: const express = require('express'); const app = express(); app.use(express.json()); app.get('/api/users', (req, res) => { res.json([{ id: 1, name: 'Alice' }]); }); app.listen(3000, () => console.log('Server running'));

Example code

Using Express.js, you can quickly set up routes and logic. 📌 Example: const express = require('express');
const app = express(); app.use(express.json()); app.get('/api/users', (req, res) => { res.json([{ id: 1, name: 'Alice' }]); }); app.listen(3000, () => console.log('Server running'));

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: Validate file types and sizes. Store files outside of the web root. Use libraries like multer. Scan files for malware. REST API & Web Development

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()); pp.get('/api/users', (req, res) => { res.json([{ id: 1, name: 'Alice' }]); }); pp.listen(3000, () => console.log('Server running')); pp.use(express.json()); pp.get('/api/users', (req, res) => { res.json([{ id: 1, name: 'Alice' }]); }); pp.listen(3000, () => console.log('Server running')); Real-world example… (ShopNest) Express…… middleware authenticates JWT, then the /orders route handler…

Explain a bit more

creates the order. pp.use(express.json()); pp.get('/api/users', (req, res) => { res.json([{ id: 1, name: 'Alice' }]); }); pp.listen(3000, () => console.log('Server running')); pp.use(express.json()); pp.get('/api/users', (req, res) => { res.json([{ id: 1, name: 'Alice' }]); }); pp.listen(3000, () => console.log('Server running')); 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 query parameters like ?page=2&limit=10 to return chunks of data instead of all at once.

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: Routing refers to defining how the application responds to different HTTP methods and URLs. 📌

Example code

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