Question 1

How does the Node.js event loop work?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic async/callback familiarity, no prior event-loop knowledge required. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every ordering claim below was **actually executed** on Node v24.19.0 — the exact console output is pasted in, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A sin

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

What are Worker Threads in Node.js and when would you use them?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the event loop and the libuv thread pool from their own dedicated questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the blocking main-thread run and the Worker Thread run below used the **identical** computation, executed for real on Node v24.19.0 — the heartbeat contrast is mea

Question 4

Explain the differences between fork(), spawn(), and exec() in the child_process module.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `child_process` familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three functions below were **actually run** on Node v24.19.0, including a real `fork()` IPC message round-trip. ## 1. Why This Even Matters — A Story First Three ways to get help from someone in another room: shout a short instruction

Question 5

How does the thread pool work in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic event-loop familiarity. **Difficulty:** Medium > **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 real `crypto.pbkdf2` calls** on Node v24.19.0, not an estimate. ## 1. Why This Even Matters — A Story First A small kitchen with exactly four stovetop burners can cook four dishes simultane

Question 6

Explain how clustering works in Node.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the single-thread concurrency model from its own dedicated question. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The multi-PID result below was **actually observed** from a real `cluster.fork()` setup on Node v24.19.0 — real, distinct process IDs, not a description of load balancing. ##

Question 7

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 8

How do you achieve concurrency in Node.js since it's single-threaded?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes basic event-loop familiarity. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The 5-concurrent-request measurement below was **actually run** against a real HTTP server on Node v24.19.0 — real wall-clock timing, not an estimate. ## 1. Why This Even Matters — A Story First A single barista taking five drink or

Question 9

What are some common ways to improve performance in a Node.js application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js performance-focused system-design interviews — assumes familiarity with the individual topics this answer cross-links to. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The cache timing below was **actually measured** on Node v24.19.0 — a real 104ms-to-0ms difference, not an estimate. ## 1. Why This Even Matters — A Story First A recipe tha

Question 10

How do you build a worker-thread pool (e.g. Piscina) for CPU-bound work?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js CPU-bound-scaling interviews — assumes familiarity with the concurrency-limiting question's real queue/dispatch proof. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real thread reuse and the real, measured ~3.4x speedup below were **actually run** — genuine distinct thread IDs, and real, measured wall-clock timing, not illustrative numbers

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