Node.js & Express

Node.js, Express, Fastify, NestJS, Bun, Deno

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Test yourself: Top 30 easy Node.js & Express interview questions →Multiple choice, with the correct answer and why it is correct on every question. Free, no sign-in.

Easy interview questions in Node.js & Express, page 2

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Unit, integration, and E2E tests explained

Unit tests isolate one function with dependencies mocked, integration tests exercise several units together (route plus DB), E2E tests drive the whole running system.

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Writing a basic Jest unit test

Import the function, group cases with describe, define each case with it or test, assert with expect and a matcher like toBe, covering normal and edge inputs.

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Purpose of Helmet middleware in Express

Helmet sets safe response headers like X-Content-Type-Options, HSTS, and CSP, mitigating MIME-sniffing, clickjacking, and protocol downgrade.

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Preventing XSS when rendering user content in templates

The risk is XSS; default to escaped interpolation (EJS <%= %>, Pug #{}) so HTML is encoded, and avoid raw output (<%- %>) for untrusted data.

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What is a Node.js Stream and why use one

A stream processes data in chunks over time, so memory stays bounded and work starts before all data arrives; ideal for large files and network IO.

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Purpose of the Node.js cluster module

Cluster forks worker processes sharing one listening port, so requests spread across CPU cores via the OS, raising throughput and adding resilience.

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HTTP request-response versus WebSocket connections?

HTTP is request-initiated, pull-based, client waits for response. WebSocket is persistent, bidirectional, either side sends data anytime.

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Socket.IO emit methods: socket, io, broadcast differences?

Socket.emit() sends to one client, broadcast.emit() to all except sender, io.emit() to all.

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How to add Socket.IO to an Express application?

Create HTTP server with express(), attach Socket.IO to it, listen on server not app, define event handlers.

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Environment configuration and secrets management in Node.js?

Use environment variables, load from .env file (dev only), never commit secrets.

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What does PM2 do for Node.js applications?

PM2 restarts crashed processes and manages multiple workers.

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How does NODE_ENV=production change Express behavior?

NODE_ENV is a convention signal, production disables verbose logging and enables caching.

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