Question 1

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 2

Explain how modules work in Node.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic JavaScript familiarity, no prior module-system knowledge required. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The caching behavior below was **actually verified** on Node v24.19.0 — a real file's body executed once across two `require()` calls, not assumed from documentation. ## 1. Why This Even Matters —

Question 3

What are the main security risks of using the 'eval()' function in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js security-focused phone screens — no prior security background assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every consequence below was **actually demonstrated by running real code**, not described as a hypothetical. ## 1. Why This Even Matters — A Story First Handing a stranger a blank check with your signature already on it is fun

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

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 7

What is the use of the 'os' module in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior systems-programming background assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every value below was **read directly from this real machine**, not written as a generic placeholder example. ## 1. Why This Even Matters — A Story First A moving crew arriving at an unfamiliar building first checks a few basic fact

Question 8

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 9

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 10

Explain the purpose of `package.json` and `npm`.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior npm experience assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The file contents below came from **actually running** `npm init -y` and `npm install` on this machine, not a hand-written example. ## 1. Why This Even Matters — A Story First A shopping list says "a loaf of bread" — not the specific loaf, not whic

NODE.JSDECODED.

Easy

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

Explain how modules work in Node.js.

What are the main security risks of using the 'eval()' function in Node.js?

What is Node.js and why is it popular?

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

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

What is the use of the 'os' module in Node.js?

Explain the concept of REPL in Node.js

Medium

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

What are npm workspaces and how do you manage a monorepo with them?

What is the difference between "type": "module", .mjs, and .cjs?

What is top-level await and what are its caveats in Node.js ESM?

What are the differences between npm, Yarn, and pnpm?

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

What is undici and why is the global fetch built on it in modern Node.js?

What is `node:sqlite`, Node's built-in SQLite module?

Hard

How do you handle circular dependencies in Node.js?

How does CommonJS `require()` an ES Module in modern Node.js?

What is diagnostics_channel and when would you use it?

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

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