Question 1

What is the role of the V8 JavaScript engine in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior engine-internals knowledge assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The version number below was read directly from a running Node process, not quoted from memory. ## 1. Why This Even Matters — A Story First A car's engine and its dashboard, seatbelts, and cargo hold are built by different teams for dif

Question 2

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 3

Explain the concept of 'event-driven architecture' in Node.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes `EventEmitter` basics 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 subscriber-addition demonstration below was **actually run** on Node v24.19.0 — the fourth subscriber genuinely started receiving events with zero changes to the publisher, not a description of expected

Question 4

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 5

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 6

How does Node.js handle crypto operations efficiently without blocking the event loop?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic event-loop and thread-pool familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the frozen and the free heartbeat below were **actually measured** on Node v24.19.0, using the identical computation in both cases. ## 1. Why This Even Matters — A Story First A single cashier who personally walks to a back

Question 7

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

Question 8

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 9

Explain the Node.js event loop.

Accepted Answer

The **event loop** is the heart of Node's concurrency: a single thread that repeatedly runs queued callbacks across ordered **phases** (timers → pending → poll → check → close). Between phases (and after each callback) it drains the **microtask** queues (process.nextTick, then Promises). This lets one thread juggle many async operations without blocking.

Question 10

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

NODE.JSDECODED.

Easy

What is the role of the V8 JavaScript engine in Node.js?

Medium

How does the Node.js event loop work?

Explain the concept of 'event-driven architecture' in Node.js.

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

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

How does Node.js handle crypto operations efficiently without blocking the event loop?

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

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

Explain the Node.js event loop.

Hard

What is `process.nextTick()` and `setImmediate()` and when to use them?

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

What changes for a Node.js app running on AWS Lambda vs a long-running server?

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

Explain the concept of 'Event Loop Pollution' and how to avoid it.

Describe the Node.js architecture.

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

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