Question 1

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 2

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 3

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js production-operations and system-design interviews — assumes familiarity with the memory-leaks question's real growth-pattern proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The memory numbers below are **real, captured output** from `node --expose-gc` on this machine — not illustrative placeholder numbers. ## 1. Why This Even Matters

Question 4

Describe the `Buffer` class in Node.js and its use cases.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes very basic binary-data familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The copy-vs-view distinction below was **actually verified** on Node v24.19.0 — a real mutation, and a real observed effect (or lack of one), not a description of expected behavior. ## 1. Why This Even Matters — A Story First A photocopy

Question 5

Fastify vs Express — how do they differ in architecture and performance?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js backend interviews — assumes basic Express familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Section 3 is a **real Fastify 5.12.4 server, actually run** across five variations of the same schema — and running all five is what corrected a wrong first guess before it went into this doc. See the note there. ## 1. Why This Even Matters

Question 6

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic garbage-collection familiarity. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every memory number below came from **actually running the allocation and reading `process.memoryUsage()`** on Node v24.19.0, not an estimate. ## 1. Why This Even Matters — A Story First A warehouse never runs out of space because items g

Question 7

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js event-loop interviews — assumes basic `setTimeout`/`setInterval` familiarity. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every timing number below came from **actually running each script and measuring real process exit time and real tick timestamps** on Node v24.19.0. ## 1. Why This Even Matters — A Story First A house is considered "occ

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