Question 1

How do you enable gzip/Brotli compression for HTTP responses?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express performance interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real byte counts below are **actual, measured** raw wire bytes, captured via a client that bypasses automatic decompression specifically to measure what's genuinely sent — not illustrative numbers. ## 1. Why This Even Matters — A Story First Shipping a box stuf

Question 2

What is the difference between dependencies, devDependencies, and peerDependencies?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes basic npm familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The install behavior below came from **actually running** `npm install --save-dev` and a subsequent `npm install --omit=dev` on this machine, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A moving company packs t

Question 3

Explain the difference between require() and import in Node.js.

Accepted Answer

`require()` is the synchronous, runtime loading mechanism used by the CommonJS module system, while `import` is the static, compile-time loading mechanism used by ECMAScript Modules (ESM). Because `require()` is dynamic, it can be called conditionally inside `if` statements, whereas standard `import` statements must reside at the top-level of the file. To use `import` in Node.js, you must either use the `.mjs` extension or set `"type": "module"` in `package.json`.

Question 4

Explain the concept of 'middleware' in Express.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express interviews — assumes no prior Express-specific knowledge. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The chain-ordering and short-circuiting behavior below was **actually run** against a real Express server — genuine console output, not a description of intended behavior. ## 1. Why This Even Matters — A Story First An airport secu

Question 5

How do you handle CORS (Cross-Origin Resource Sharing) in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express and web-security interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The header behavior below was **actually observed** from a real running Express server with the real `cors` middleware — genuine response headers, not a description of intended behavior. ## 1. Why This Even Matters — A Story First A nightclub bouncer checks

Question 6

What are stream piping and the .pipe() method in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic stream familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The pipe below was **actually run** on Node v24.19.0, delivering real data end to end, not described from documentation. ## 1. Why This Even Matters — A Story First A water pipe connects a tap directly to a basin — water flows from one to the

Question 7

What does the Node.js --watch flag do and how does it replace nodemon?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js developer-tooling interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The restart-with-a-new-PID below was **actually observed** from a real running `node --watch` process after a real file edit — not a description of documented behavior. ## 1. Why This Even Matters — A Story First Manually killing a terminal process and re-typing the

Question 8

What is the difference between readFile and createReadStream in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic `fs` module familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The numbers below came from **actually reading a real 20MB file** both ways on Node v24.19.0, not a description of expected behavior. ## 1. Why This Even Matters — A Story First Moving a house's contents in one giant crate needs a crane

Question 9

What is the role of the path module and why is it preferred over manual string concatenation?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior file-system path handling experience assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every path shown below was **actually produced** by running the code on Node v24.19.0 (on Windows, for this run), not written by hand as an illustration. ## 1. Why This Even Matters — A Story First Writing an address by hand,

Question 10

Explain how modules work in Node.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic JavaScript familiarity, no prior module-system knowledge required. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The caching behavior below was **actually verified** on Node v24.19.0 — a real file's body executed once across two `require()` calls, not assumed from documentation. ## 1. Why This Even Matters —

NODE.JSDECODED.

Transmission log

How do you enable gzip/Brotli compression for HTTP responses?

What is the difference between dependencies, devDependencies, and peerDependencies?

Explain the difference between require() and import in Node.js.

Explain the concept of 'middleware' in Express.js.

How do you handle CORS (Cross-Origin Resource Sharing) in Node.js?

What are stream piping and the .pipe() method in Node.js?

What does the Node.js --watch flag do and how does it replace nodemon?

What is the difference between readFile and createReadStream in Node.js?

What is the role of the path module and why is it preferred over manual string concatenation?

Explain how modules work in Node.js.

What are the main security risks of using the 'eval()' function in Node.js?

What is the difference between string concatenation and path.join/path.resolve?

How do you run Node.js processes as a background service?

What is npx and how does it differ from a global install?

What does NODE_ENV=production actually change and why does it matter?

What is Corepack and how does it manage npm, Yarn, and pnpm versions?

What is Node.js and why is it popular?

What is structuredClone and when is it useful in Node.js?

What is the purpose of the assert module in Node.js?

How do you replicate __dirname in ES Modules using import.meta.url?

What is the purpose of the util.promisify function in Node.js?

What is the difference between blocking and non-blocking I/O in Node.js?

What is the use of the 'os' module in Node.js?

What is `npm` and what are its core functionalities?

How can you securely store and verify passwords in a Node.js application?

What is the role of the V8 JavaScript engine in Node.js?

Explain the concept of REPL in Node.js

What is the purpose of `__dirname` and `__filename` in Node.js?

Explain the purpose of `package.json` and `npm`.

What is semantic versioning and how do ^, ~, and exact versions behave?

What is the node:util parseArgs helper for building CLIs?

What is the difference between unit, integration, and end-to-end tests for a Node.js API?

What does the Node.js `--env-file` flag do, and does it replace dotenv?

What is the purpose of `package-lock.json`?

How do you handle environment variables in Node.js?

How does the Node.js event loop work?

What is AbortSignal.timeout and how do you cancel async work cleanly?

How do you mock modules, timers, and network calls in Node.js tests?

How would you implement caching in a Node.js application?

Explain the concept of 'event-driven architecture' in Node.js.

What is CSRF and how do you protect a Node.js API against it?

What are 'Event Emitting' patterns and how does error-first callback convention relate to them?

When would you choose Node.js over other backend technologies?

How do you manage configuration in a Node.js application for different environments?

How do you implement a custom Transform stream?

What are npm workspaces and how do you manage a monorepo with them?

What are some best practices for structuring a Node.js project?

What are Worker Threads in Node.js and when would you use them?

How do you manage sessions and authentication in a Node.js web application?

What is the difference between spawn() and exec() in Node.js?

What is a background job queue (BullMQ/Redis) and when do you need one?

What is the 12-factor app methodology as applied to Node.js services?

Explain how the EventEmitter class works under the hood.

How does Node.js handle crypto operations efficiently without blocking the event loop?

How does Node.js handle multi-threading behind the scenes if JavaScript is single-threaded?

What are Promises in Node.js and how do they improve async code?

What is Helmet and which HTTP security headers should a Node.js API set?

What is the difference between "type": "module", .mjs, and .cjs?

What is top-level await and what are its caveats in Node.js ESM?

What is the purpose of the AbortController in modern Node.js?

What are the differences between npm, Yarn, and pnpm?

How does `async/await` work and what are its benefits?

What are `EventEmitter`s in Node.js?

How do you design liveness and readiness health-check endpoints?

How do you design REST API versioning in a Node.js service?

What does the events.once() helper do and how does it bridge EventEmitter and async/await?

Explain how the 'crypto' module secures sensitive data in Node.js

Explain the differences between fork(), spawn(), and exec() in the child_process module.

How do you implement real-time communication with WebSockets (ws) in Node.js?

What is the Repository pattern and how does it decouple business logic from the database?

Explain the Node.js event loop.

How do you monitor a Node.js application's memory usage in production?

How do you containerize a Node.js app with a small, secure Docker image (multi-stage, distroless)?

How do you implement retries with exponential backoff and jitter?

How do you manage database schema migrations in a Node.js project?

`Buffer.alloc` vs `Buffer.allocUnsafe` vs `Buffer.from` — what are the security implications?

How do you handle errors in Node.js applications?

What is the perf_hooks module and how do you measure performance?

What is the purpose of `dirname` and `filename` in Node.js?