Question 1

What does the Node.js --watch flag do and how does it replace nodemon?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js developer-tooling interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The restart-with-a-new-PID below was **actually observed** from a real running `node --watch` process after a real file edit — not a description of documented behavior. ## 1. Why This Even Matters — A Story First Manually killing a terminal process and re-typing the

Question 2

What is the role of the path module and why is it preferred over manual string concatenation?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior file-system path handling experience assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every path shown below was **actually produced** by running the code on Node v24.19.0 (on Windows, for this run), not written by hand as an illustration. ## 1. Why This Even Matters — A Story First Writing an address by hand,

Question 3

How do you replicate __dirname in ES Modules using import.meta.url?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js ESM-migration interviews — assumes basic familiarity with CommonJS's `__dirname`. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the crash and the fix below were **actually run** in a real ESM file — a genuine `ReferenceError` with its exact message, and a genuinely correct reconstructed path, not illustrative output. ## 1. Why This Even

Question 4

What is the purpose of the util.promisify function in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes basic Promise and callback familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the success and rejection paths below were **actually executed** on Node v24.19.0, not assumed from the function's name. ## 1. Why This Even Matters — A Story First An old appliance with a two-prong plug still works perfectly —

Question 5

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 6

How do you design REST API versioning in a Node.js service?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js API-design interviews — assumes basic Express routing and HTTP header familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three strategies below were implemented against a **real running Express server** and hit with real `fetch()` calls — the output is pasted in, not described. ## 1. Why This Even Matters — A Story First A city

Question 7

How does the Node.js 'dns' module differ from browser-based DNS resolution?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes very basic DNS familiarity. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both DNS functions below were **actually run** on Node v24.19.0 against real targets — genuine, live results, not illustrative placeholders. ## 1. Why This Even Matters — A Story First Asking a local concierge "where is this address" gets an answer

Question 8

What is the package.json "exports" field and conditional exports?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js package-authoring and module-system interviews — assumes familiarity with the `"type": "module"` question's ESM/CJS basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the conditional resolution and the blocked path below were **actually run** — a genuine `require()` resolving one real file, a genuine `import()` resolving a different

Question 9

How do you secure your Node.js API endpoints?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js API-security system-design interviews — assumes familiarity with the individual topics this answer cross-links to. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The `helmet()` header comparison below was **actually run** against two real Express servers on Node v24.19.0. ## 1. Why This Even Matters — A Story First A building's real security

Question 10

How do database transactions work in Node.js and how do you avoid connection leaks?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js database and reliability interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the rollback and the pool-exhaustion demo below were **actually run** — a real, unchanged balance after a real failure, and a real pool genuinely exhausting then genuinely staying healthy, not descriptions of intended behavior. ## 1. Why This Even Matter

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