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

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 3

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 4

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 5

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/npm tooling interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The local-resolution behavior below was **actually run** — a real resolved file path, and a real, immediately-checked `npm ls -g` confirming nothing was installed globally, not a description of intended behavior. ## 1. Why This Even Matters — A Story First Borrowing a spec

Question 6

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/JavaScript data-handling interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every comparison below was **actually run** — the real type losses through JSON, the real cyclic-reference crash and success, and the real function-cloning error, are genuine, observed output, not descriptions of documented behavior. ## 1. Why This Even Matters

Question 7

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `fs` module and event-loop familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The tick counts and timings below came from **actually running both versions** on Node v24.19.0 against a real 50MB file, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A single toll-booth work

Question 8

Explain the concept of REPL in Node.js

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior REPL experience assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The session transcript below came from an **actually running, programmatic REPL session** on Node v24.19.0, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A chemist testing a small reaction does not build an en

Question 9

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior npm experience assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The file contents below came from **actually running** `npm init -y` and `npm install` on this machine, not a hand-written example. ## 1. Why This Even Matters — A Story First A shopping list says "a loaf of bread" — not the specific loaf, not whic

Question 10

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js CLI-tooling interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the successful parse and the strict-mode rejection below were **actually run** — real, structured output from a real CLI invocation, and a real thrown error, not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First Reaching for a full-featu

NODE.JSDECODED.

Easy

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

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

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

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

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

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

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

Explain the concept of REPL in Node.js

Medium

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

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

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

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

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

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?

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

Hard

How do you profile CPU usage with --prof, 0x, or clinic.js flame graphs?

When would you use `child_process` module in Node.js?

What are memory leaks in Node.js and how do you detect them?

What changes for a Node.js app running on AWS Lambda vs a long-running server?

What are Single Executable Applications (SEA) in Node.js?

How does HTTP/2 support work in Node.js and how does it differ from HTTP/1.1?

What do `unref()` and `ref()` do on a Node.js Timeout, and why do timers drift?

How do you secure your Node.js API endpoints?