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 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 3

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 4

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js deployment and configuration interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the "Node core does nothing special" proof and the real Express behavior difference below were **actually run** — not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First A single word written on a sticky note ("PRODUCTION"

Question 5

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 6

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js ESM-migration interviews — assumes basic familiarity with CommonJS's `__dirname`. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the crash and the fix below were **actually run** in a real ESM file — a genuine `ReferenceError` with its exact message, and a genuinely correct reconstructed path, not illustrative output. ## 1. Why This Even

Question 7

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js dependency-management interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every range check below was **actually run** with the real `semver` package — genuine `true`/`false` results, not a description of the spec. ## 1. Why This Even Matters — A Story First A promise to "only ever make the recipe spicier or add a garnish, never change

Question 8

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

Question 9

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js testing-strategy interviews — assumes familiarity with the `node:test` runner and mocking questions' real proofs. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The timing comparison below is **real, measured** output from actually running both a unit and an integration test with `node --test` — genuine milliseconds, not illustrative numbers.

Question 10

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js async-cancellation interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the successful and the aborted operation below were **actually run** — a real, measured abort at ~304ms for a configured 300ms timeout, and a real, specific error, not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First Setting a

NODE.JSDECODED.

Easy

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

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

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 structuredClone and when is it useful in Node.js?

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

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

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

Medium

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 do you implement a custom Transform stream?

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

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?

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

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

Hard

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

What is a ReDoS (Regular Expression Denial of Service) attack and how do you avoid it?

What is diagnostics_channel and when would you use it?

How do you implement a circuit breaker for unreliable downstream services?

What is SSRF and how do you mitigate it in a Node.js backend?

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 are the Web Streams API (ReadableStream/WritableStream) in Node.js and how do they differ from node:stream?