Question 1

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 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

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 4

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 5

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic file-path familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The values below were printed from a **real file on disk**, deliberately not from `node -e`, which was checked first and produces misleading placeholder values instead. ## 1. Why This Even Matters — A Story First A person gives directions

Question 6

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js backend interviews — assumes basic `process.env` familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Everything below was **executed against Node v24.19.0** — the raw output is pasted in section 3. ## 1. Why This Even Matters — A Story First For years, every Node tutorial opened the same way: npm install dotenv, then

Question 7

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js testing interviews — assumes familiarity with the `node:test` runner question's real pass/fail proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three mocking mechanisms below were **actually run** — a real 10-second timer genuinely fired in under 1ms, and a real method mock genuinely avoided a real network call, not descriptions of i

Question 8

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes familiarity with both `EventEmitter` basics and error-first callbacks individually, connecting the two. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The silent-swallow-versus-throw contrast below was **actually run** on Node v24.19.0 — a real absence of a crash in one case, a real caught exception in the other. ## 1. W

Question 9

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js tooling and monorepo-architecture interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The symlink creation and cross-package resolution below were **actually run** — a real `npm install`, real `ls -la` output confirming genuine symlinks, and a genuine live-edit visible through them. ## 1. Why This Even Matters — A Story First Two roo

Question 10

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/JavaScript interviews — assumes basic Promise familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every claim below — including that an async function's return value really is a Promise — was **actually executed and inspected**, not assumed from how the syntax reads. ## 1. Why This Even Matters — A Story First A recipe written as "w

NODE.JSDECODED.

Easy

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?

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

Explain the concept of REPL in Node.js

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

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

Medium

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

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

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

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

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

How do you protect a Node.js API against Denial of Service (DoS) and brute-force attacks?

What are Node.js Streams and when would you use them?

How do you run TypeScript directly in Node.js (native type stripping, tsx, ts-node)?

Hard

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

What is the 'vm' (Virtual Machine) module and when would you use it?