Question 1

What is the purpose of the assert module in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic testing/assertion familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both outcomes below were **actually executed** on Node v24.19.0 — the exact thrown error message is pasted in, not paraphrased. ## 1. Why This Even Matters — A Story First A smoke detector makes no sound at all when the air is clea

Question 2

Explain the concept of REPL in Node.js

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior REPL experience assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The session transcript below came from an **actually running, programmatic REPL session** on Node v24.19.0, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A chemist testing a small reaction does not build an en

Question 3

What is the purpose of `__dirname` and `__filename` in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic file-path familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The values below were printed from a **real file on disk**, deliberately not from `node -e`, which was checked first and produces misleading placeholder values instead. ## 1. Why This Even Matters — A Story First A person gives directions

Question 4

What is the difference between unit, integration, and end-to-end tests for a Node.js API?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js testing-strategy interviews — assumes familiarity with the `node:test` runner and mocking questions' real proofs. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The timing comparison below is **real, measured** output from actually running both a unit and an integration test with `node --test` — genuine milliseconds, not illustrative numbers.

Question 5

How do you mock modules, timers, and network calls in Node.js tests?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js testing interviews — assumes familiarity with the `node:test` runner question's real pass/fail proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three mocking mechanisms below were **actually run** — a real 10-second timer genuinely fired in under 1ms, and a real method mock genuinely avoided a real network call, not descriptions of i

Question 6

What is the Repository pattern and how does it decouple business logic from the database?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js architecture and testing interviews — assumes familiarity with the unit-vs-integration-testing question's real speed-comparison proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The identical business logic running against two real, different backing stores below was **actually executed** — real, correct output from both, plus a real sour

Question 7

What is the built-in node:test runner and how does it compare to Jest and Mocha?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js testing-strategy interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The pass/fail run below was **actually executed** with `node --test` on a real file — a genuine assertion diff and a genuine exit code, not illustrative output. ## 1. Why This Even Matters — A Story First Carrying a full toolbox to tighten one screw is often more setu

Question 8

How does HTTP/2 support work in Node.js and how does it differ from HTTP/1.1?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js networking and HTTP-performance interviews. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real, measured timing comparison below was **actually run** with Node's real, built-in `http2` and `http` modules — genuine elapsed times from a real 5-concurrent-request workload, not descriptions of documented behavior. ## 1. Why This Even Matters

Question 9

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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