Interview Q&A

Short answer: Node.js runs on a single thread by default, which means it can handle only one operation at a time per process. Clustering allows you to create multiple Node.js processes (workers) that share the same server port. This way, your app can utilize multiple CPU cores and handle more requests concurrently. 📌 Example: Using the built-in cluster module, you can fork multiple workers.

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: sync function connect() { const uri = 'mongodb://localhost:27017/mydatabase'; const client = new MongoClient(uri); try { wait client.connect(); console.log('Connected to MongoDB'); const db = client.db('mydatabase'); // Use `db` to query collections } catch (err) { console.error(err); } finally { wait client.close(); } } connect(); Example… code sync…… function connect() { const uri =…

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'mongodb://localhost:27017/mydatabase'; const client = new MongoClient(uri); try { wait client.connect(); console.log('Connected to MongoDB'); const db = client.db('mydatabase'); // Use `db` to query collections } catch (err) { console.error(err); } finally { wait client.close(); } } connect(); sync function connect() { const uri = 'mongodb://localhost:27017/mydatabase'; const client = new MongoClient(uri); try { wait client.connect(); console.log('Connected to MongoDB'); const db = client.db('mydatabase'); // Use `db` to query collections } catch (err) { console.error(err); } finally { wait client.close(); } } connect(); Example… code sync function…

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: time per process. Clustering allows you to create multiple Node.js processes (workers) that share the same server port. This way, your app can utilize multiple CPU cores and handle more requests concurrently. 📌 Example: Using the built-in cluster module, you can fork multiple workers.

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 is an open-source, cross-platform runtime environment that allows you to run JavaScript on the server side. It’s built on the V8 JavaScript engine developed by Google (the same one used in Chrome). With Node.js, you can build scalable and high-performance web applications, APIs, and even real-time services like chat apps. 📌

Example code

If you write a simple HTTP server in Node.js, you can serve a webpage without using a traditional web server like Apache: const http = require('http'); http.createServer((req, res) => { res.end('Hello from Node.js server!'); }).listen(3000);

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: How do you create and use custom events? EventEmitter allows objects to emit named events and listen for them. Example: const EventEmitter = require('events'); const emitter = new EventEmitter(); emitter.on('greet', (name) => { console.log(`Hello, ${name}!`); }); emitter.emit('greet', 'Alice'); Output: Hello, Alice! It’s fundamental for asynchronous communication in Node.js.

Example code

How do you create and use custom events? EventEmitter allows objects to emit named events and listen for them. Example: const EventEmitter = require('events');
const emitter = new EventEmitter(); emitter.on('greet', (name) => { console.log(`Hello, ${name}!`); }); emitter.emit('greet', 'Alice'); Output: Hello, Alice! It’s fundamental for asynchronous communication 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: EventEmitter allows objects to emit named events and listen for them.

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! const emitter = new EventEmitter(); emitter.on('greet', (name) => { console.log(`Hello, ${name}!`); }); emitter.emit('greet', 'Alice'); Output: Hello, Alice! It’s fundamental for asynchronous communication 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: Process management means keeping your app running reliably, restarting it if it crashes, and managing multiple instances. PM2 is a popular Node.js process manager that: Restarts apps on crashes or code changes Manages clustering (multi-core usage) Offers logs and monitoring dashboards Supports zero-downtime reloads Run your app with PM2 like this: pm2 start app.js pm2 monit

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: Mongoose is an ODM (Object Data Modeling) library for MongoDB in Node.js. It provides: Schema-based data modeling Validation Middleware (hooks) Easy querying and relationship management You define schemas and models to interact with MongoDB more intuitively.

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 mongoose = require('mongoose'); const userSchema = new mongoose.Schema({ name: { type: String, required: true }, email: { type: String, required: true, unique: true }, age: Number, createdAt: { type: Date, default: Date.now } }); const User = mongoose.model('User', userSchema); // Usage example async function createUser() { const user = new User({ name: 'Alice', email: 'alice@example.com', age: 25 }); await…

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user.save(); console.log('User saved'); }

Example code

const mongoose = require('mongoose'); const userSchema = new mongoose.Schema({ name: { type: String, required: true }, email: { type: String, required: true, unique: true }, age: Number, createdAt: { type: Date, default: Date.now } }); const User = mongoose.model('User', userSchema); // Usage example async function createUser() { const user = new User({ name: 'Alice', email: 'alice@example.com', age: 25 }); await user.save(); console.log('User saved'); }

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: Mocha is a test runner that executes your test files, organizes tests in suites (describe), and allows async testing. It does not provide assertions, so it’s often paired with assertion libraries like Chai.

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: ge: Number, createdAt: { type: Date, default: Date.now } }); const User = mongoose.model('User', userSchema); // Usage example sync function createUser() { const user = new User({ name: 'Alice', email: 'alice@example.com', ge: 25 }); wait user.save(); console.log('User saved'); } ge: Number, createdAt: { type: Date, default:… Date.now } }); const User =…… mongoose.model('User', userSchema); // Usage example sync…

Explain a bit more

function createUser() { const user = new User({ name: 'Alice', email: 'alice@example.com', ge: 25 }); wait user.save(); console.log('User saved'); } ge: Number, createdAt: { type: Date, default: Date.now } }); const User = mongoose.model('User', userSchema); // Usage example sync function createUser() { const user = new User({ name: 'Alice', email: 'alice@example.com', ge: 25 }); wait user.save(); console.log('User saved'); } ge: Number, createdAt: { type: Date, default:… Date.now } }); const User = mongoose.model('User', userSchema); // Usage example sync function createUser() { const user = new User({ name: 'Alice', email:…

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: And allows async testing. It does not provide assertions, so it’s often paired with assertion libraries like Chai.

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: PM2 is a popular production process manager for Node.js applications. It helps you: Manage and keep apps alive forever (auto-restart on crashes). Run apps in cluster mode easily. Monitor resource usage (CPU, memory). Handle zero-downtime reloads. npm install pm2 -g pm2 start app.js -i max # Runs in cluster mode with max CPU cores

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: The V8 engine is a high-performance JavaScript engine developed by Google for Chrome. Node.js uses it to compile and run JavaScript code on the server side. It converts JS code into machine code, making it fast and efficient. 📌 Use Case: When you run a .js file with Node.js, the V8 engine compiles your code into machine code behind the scenes.

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: Helmet is a middleware that sets HTTP headers to protect against common attacks: Adds Content Security Policy (CSP) Prevents MIME sniffing Protects against clickjacking Enables HSTS (HTTPS enforcement) Usage: const helmet = require('helmet'); app.use(helmet());

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: Chai is an assertion library for Node.js that lets you write readable tests with different styles: Expect style (most popular): expect(result).to.equal(5); Should style: result.should.equal(5); Assert style: assert.equal(result, 5);

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: Load balancing distributes incoming requests across multiple server instances to: Improve performance Increase availability and fault tolerance In Node.js, you can: Use the cluster module to spawn workers on multiple CPU cores. Use external load balancers like Nginx, HAProxy, or cloud load balancers. PM2 also supports clustering with: pm2 start app.js -i max

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: ssert style: ssert.equal(result, 5); ssert style: ssert.equal(result, 5); ssert style: ssert.equal(result, 5); ssert style: ssert.equal(result, 5); ssert style: ssert.equal(result, 5); ssert style: ssert.equal(result, 5); ssert style: ssert.equal(result, 5); ssert style: ssert.equal(result, 5);

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: PUT: Replaces the entire resource with the data sent. If a field is missing in the request, it may get erased. Idempotent (same request repeated yields same result). PATCH: Applies partial updates to the resource. Only changes the fields specified. Not necessarily idempotent.

Example code

Updating user email. PUT /users/1 with { "name": "Alice" } replaces whole user — email might get removed. PATCH /users/1 with { "email": "new@example.com" } updates just the email.

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: Sequelize is a popular ORM for relational databases like MySQL, PostgreSQL, SQLite, and MSSQL. It allows you to: Define models with JavaScript classes Handle migrations and schema changes Write complex queries using JavaScript instead of raw SQL

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: Supertest is a library for testing HTTP APIs, especially Express apps. It allows you to simulate HTTP requests and assert on responses. Example: const request = require('supertest');

Example code

const app = require('../app'); // Your Express app describe('GET /users', () => { it('should return 200 and a list of users', (done) => { request(app) .get('/users') .expect(200) .expect('Content-Type', /json/) .end((err, res) => { if (err) return done(err); done(); }); }); });

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: The event loop is the core of Node.js's non-blocking I/O operations. It handles all asynchronous operations in a single thread, constantly checking for events (e.g., incoming data, timers) and executing associated callbacks. 📌

Example code

setTimeout(() => { console.log('Executed after 2 seconds'); }, 2000); This callback is scheduled by the event loop and executed when the time is up.

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: Backpressure happens when data is produced faster than it can be consumed downstream. In Node.js streams, it's a built-in mechanism to: Pause the readable stream when the writable stream is overwhelmed. Prevent memory overload and crashes. This flow control allows producers and consumers to work in sync.

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: Service Principal is a security identity for apps or automation. Used for authentication in scripts, CI/CD pipelines, and service-to-service communication. Example – Azure CLI login: az login --service-principal -u <appId> -p <password> --tenant <tenantId>

Real-world example (ShopNest)

ShopNest on Azure typically uses App Service + SQL Database + Blob Storage + Application Insights for monitoring.

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: Azure AD roles – Manage identity and directory-level permissions (e.g., User Administrator, Global Admin) Azure RBAC – Manage resource-level permissions (e.g., Reader, Contributor, Owner) Both work together to enforce security and access control in Azure.

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.