Question 1

What is the perf_hooks module and how do you measure performance?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js performance-measurement interviews — assumes familiarity with the CPU-profiling question's real hot-function identification. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The cross-validated timing below is **real, measured** output — two genuinely independent measurement mechanisms agreeing closely on the actual real duration, not illustrat

Question 2

How do you implement structured logging with pino or winston, and why avoid console.log in production?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js observability and production-logging interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the real structured output and the real level-filtering below were **actually run** with the real `pino` library — genuine, parseable JSON, and a genuine, confirmed suppression, not descriptions of documented behavior. ## 1. Why This Even Mat

Question 3

How do you handle uncaught exceptions and unhandled promise rejections in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic Promise/async familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the handled and the genuinely unhandled (crashing) cases below were **actually executed** on Node v24.19.0 — a real exit code, not an assumption. ## 1. Why This Even Matters — A Story First A building has two entirely separate emergency

Question 4

What is diagnostics_channel and when would you use it?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js observability and library-design interviews. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real gated pub/sub behavior below was **actually run** — a genuine, confirmed `hasSubscribers` state change, and real events genuinely reaching a subscriber only after it attached, not descriptions of documented behavior. ## 1. Why This Even Matters

Question 5

What is AsyncLocalStorage and what problem does it solve?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js async-architecture interviews — assumes familiarity with the event-loop and Promise-fundamentals questions in this bank. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The concurrent, interleaved context isolation below was **actually run** — two real requests genuinely overlapping in time, each retaining the correct context, not a description

Question 6

How do you add OpenTelemetry distributed tracing to a Node.js service?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js observability and distributed-systems interviews — assumes familiarity with the structured-logging question's real, complementary proof. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real, correlated spans below were **actually created and exported** — a genuine shared trace ID, a genuine, confirmed parent-child relationship, and real, mea

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