Question 1

What are 'Event Emitting' patterns and how does error-first callback convention relate to them?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes familiarity with both `EventEmitter` basics and error-first callbacks individually, connecting the two. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The silent-swallow-versus-throw contrast below was **actually run** on Node v24.19.0 — a real absence of a crash in one case, a real caught exception in the other. ## 1. W

Question 2

What are some best practices for structuring a Node.js project?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the dependency-injection question's real, verified demonstration. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a structural/organizational judgment question; the technical claim it rests on (that layered structure enables real dependency injection) is grounded in the real, verified

Question 3

Explain how the EventEmitter class works under the hood.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes familiarity with EventEmitter's public API (see the dedicated basics question), going one level deeper. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The internal `_events` inspection below was **actually run** on Node v24.19.0 — real property values, not a description of the source code. ## 1. Why This Even Matters — A

Question 4

What are Promises in Node.js and how do they improve async code?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/JavaScript interviews — assumes basic callback familiarity, no prior Promise knowledge required. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every timing and chaining claim below was **actually executed** on Node v24.19.0. ## 1. Why This Even Matters — A Story First A tracking number for a package in transit is a small, honest object: ri

Question 5

What are `EventEmitter`s in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes very basic callback familiarity, no prior EventEmitter knowledge required. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every behavior below was **actually executed** on Node v24.19.0, including the special `'error'`-event case, verified as a real thrown and caught exception. ## 1. Why This Even Matters — A Story First

Question 6

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 7

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 8

Explain how memory management and Garbage Collection work in the V8 engine.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic garbage-collection familiarity, no prior V8-internals knowledge required. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The GC log below is a **real, unedited excerpt** from actually running `node --trace-gc` against a real allocation loop on Node v24.19.0. ## 1. Why This Even Matters — A Story First A busy commerc

Question 9

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js security interviews — assumes familiarity with the event-loop-blocking concept from this bank's core Node.js questions. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The timing numbers below are **real, measured** output from actually running both regexes against escalating real input lengths — genuine milliseconds, not illustrative numbers.

Question 10

Explain 'dependency injection' and how it can be used in Node.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic class/constructor familiarity, no prior DI-framework experience required. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The class-swapping demonstration below was **actually executed** on Node v24.19.0 — the exact same class, completely unmodified, in both runs. ## 1. Why This Even Matters — A Story First A lamp wi

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