Question 1

What is Node.js and why is it popular?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior Node knowledge assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The version numbers below were read directly from a running Node process on this machine, not quoted from memory. ## 1. Why This Even Matters — A Story First Before Node.js, JavaScript lived almost entirely in one place: the browser, running whatev

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

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js real-time-communication interviews — assumes familiarity with the SSE question's real one-directional streaming proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real server push and the real client/server message exchange below were **actually run** — genuine, unsolicited server-initiated data, not a description of the protocol's doc

Question 4

How do you implement Server-Sent Events (SSE) in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js real-time-communication interviews — assumes familiarity with the WebSockets question's real bidirectional proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real events below were **actually streamed** from a real server to a real client over one connection — genuine timestamps roughly 100ms apart, not a single buffered response. ##

Question 5

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

NODE.JSDECODED.

Easy

What is Node.js and why is it popular?

Medium

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

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

How do you implement Server-Sent Events (SSE) in Node.js?

Hard

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