Question 1

What is the difference between dependencies, devDependencies, and peerDependencies?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes basic npm familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The install behavior below came from **actually running** `npm install --save-dev` and a subsequent `npm install --omit=dev` on this machine, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A moving company packs t

Question 2

Explain the difference between require() and import in Node.js.

Accepted Answer

`require()` is the synchronous, runtime loading mechanism used by the CommonJS module system, while `import` is the static, compile-time loading mechanism used by ECMAScript Modules (ESM). Because `require()` is dynamic, it can be called conditionally inside `if` statements, whereas standard `import` statements must reside at the top-level of the file. To use `import` in Node.js, you must either use the `.mjs` extension or set `"type": "module"` in `package.json`.

Question 3

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 4

What is Node.js and why is it popular?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior Node knowledge assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The version numbers below were read directly from a running Node process on this machine, not quoted from memory. ## 1. Why This Even Matters — A Story First Before Node.js, JavaScript lived almost entirely in one place: the browser, running whatev

Question 5

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 6

What is the role of the V8 JavaScript engine in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior engine-internals knowledge assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The version number below was read directly from a running Node process, not quoted from memory. ## 1. Why This Even Matters — A Story First A car's engine and its dashboard, seatbelts, and cargo hold are built by different teams for dif

Question 7

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 8

How do you handle environment variables in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior configuration-management experience assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The string-coercion behavior below was **actually verified** on Node v24.19.0, not assumed from how JavaScript "usually" handles types. ## 1. Why This Even Matters — A Story First A form field that only accepts typed text will

Question 9

How do you containerize a Node.js app with a small, secure Docker image (multi-stage, distroless)?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js deployment/DevOps-adjacent system-design interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The production-vs-full dependency size gap below was **actually measured** in this sandbox via real `npm install` runs. The full Docker image build itself could not be executed in this particular sandbox session (Docker Desktop's engine was not

Question 10

`Buffer.alloc` vs `Buffer.allocUnsafe` vs `Buffer.from` — what are the security implications?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js low-level/security interviews — assumes basic Buffer and typed-array familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every number and byte sequence below came from **actually running the code** on Node v24.19.0, across repeated executions — including an honest note on what I could and could not reproduce. ## 1. Why This Even Matt

NODE.JSDECODED.

Easy

What is the difference between dependencies, devDependencies, and peerDependencies?

Explain the difference between require() and import in Node.js.

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

What is Node.js and why is it popular?

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

What is the role of the V8 JavaScript engine in Node.js?

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

How do you handle environment variables in Node.js?

Medium

How do you containerize a Node.js app with a small, secure Docker image (multi-stage, distroless)?

`Buffer.alloc` vs `Buffer.allocUnsafe` vs `Buffer.from` — what are the security implications?

How do you run TypeScript directly in Node.js (native type stripping, tsx, ts-node)?

What are some common security best practices in Node.js applications?

Hard

How do you handle circular dependencies in Node.js?

When would you use `child_process` module in Node.js?

What changes for a Node.js app running on AWS Lambda vs a long-running server?

What are Single Executable Applications (SEA) in Node.js?

Describe the Node.js architecture.

What is the role of `libuv` in Node.js?

What is the Node.js permission model (--permission) and what does it protect against?