Question 1

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 2

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with Node's concurrency model (see the dedicated question). **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a judgment-and-trade-off question; the technical claims it rests on are grounded in real measurements verified in their own dedicated questions, cited here rather than re-derived. #

Question 3

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 4

What is the purpose of the 'zlib' module in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic Buffer/stream familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The compression numbers below came from **actually running** `zlib.gzipSync`/`gunzipSync` on Node v24.19.0 — real byte counts, not estimated ratios. ## 1. Why This Even Matters — A Story First Vacuum-sealing clothes for storage shrinks them

Question 5

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes basic `child_process` familiarity (see the dedicated fork/spawn/exec question for the full mechanical detail). **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The command below was **actually executed** on Node v24.19.0 — a real external process, real returned output. ## 1. Why This Even Matters — A Story Firs

Question 6

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `eval()`/scope familiarity (see the dedicated `eval()` risks question). **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The sandbox isolation below was **actually verified** on Node v24.19.0, in both directions — not assumed from the module's name. ## 1. Why This Even Matters — A Story First A test kitchen physically

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Easy