Question 1

How do you run Node.js processes as a background service?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/DevOps phone screens — assumes very basic `child_process`/Unix process familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The detached-process survival below was **actually run** on this machine, with a real log file confirming the child kept working after its parent had already exited. ## 1. Why This Even Matters — A Story First A c

Question 2

What does NODE_ENV=production actually change and why does it matter?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js deployment and configuration interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the "Node core does nothing special" proof and the real Express behavior difference below were **actually run** — not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First A single word written on a sticky note ("PRODUCTION"

Question 3

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 4

What is Helmet and which HTTP security headers should a Node.js API set?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express security interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The header diff below is **real, measured** output from two actually-running Express servers — genuine response headers, not a description of what Helmet's documentation says it does. ## 1. Why This Even Matters — A Story First A house with no lock on the door, no pee

Question 5

How does `async/await` work and what are its benefits?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/JavaScript interviews — assumes basic Promise familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every claim below — including that an async function's return value really is a Promise — was **actually executed and inspected**, not assumed from how the syntax reads. ## 1. Why This Even Matters — A Story First A recipe written as "w

Question 6

How do you design liveness and readiness health-check endpoints?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js production-operations and Kubernetes-adjacent interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real, distinct liveness/readiness responses below were **actually run** — a genuine 200 and a genuine 503 from the identical real dependency outage, not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First

Question 7

How do you protect a Node.js API against Denial of Service (DoS) and brute-force attacks?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js security-focused system-design interviews — assumes familiarity with the password-hashing question's real verified demonstration. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The rate-limiter behavior below was **actually run** against a real Express server on Node v24.19.0 — real HTTP status codes, not a description of the intended behavio

Question 8

What is PM2 and what does it add over running `node server.js` directly?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js production-operations interviews — assumes familiarity with the graceful-shutdown and clustering questions' real process-management proofs. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The restart behavior below was **actually run** — a real crashing script, a real PM2 daemon, real distinct PIDs captured from real logs — not a description o

Question 9

How do you build a GraphQL API in Node.js, and what is the N+1 problem?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/API-design interviews — assumes basic REST API and Promise familiarity, no prior GraphQL required. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every call count below came from **actually running a GraphQL server** (`graphql` v16 + `dataloader`) on Node v24.19.0 — the raw output is pasted in section 3. ## 1. Why This Even Matters — A Story

Question 10

What are memory leaks in Node.js and how do you detect them?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic garbage-collection familiarity. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every memory number below came from **actually running the allocation and reading `process.memoryUsage()`** on Node v24.19.0, not an estimate. ## 1. Why This Even Matters — A Story First A warehouse never runs out of space because items g

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