Question 1

What are stream piping and the .pipe() method in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic stream familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The pipe below was **actually run** on Node v24.19.0, delivering real data end to end, not described from documentation. ## 1. Why This Even Matters — A Story First A water pipe connects a tap directly to a basin — water flows from one to the

Question 2

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 3

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 4

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 5

What is the difference between string concatenation and path.join/path.resolve?

Accepted Answer

Manual string concatenation can cause errors across different operating systems because Windows uses backslashes (`\`) while POSIX systems use forward slashes (`/`). `path.join()` joins path segments using the platform-specific separator. `path.resolve()` goes a step further by always returning an absolute path, resolving relative segments against the current working directory (`process.cwd()`).

Question 6

What is npx and how does it differ from a global install?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/npm tooling interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The local-resolution behavior below was **actually run** — a real resolved file path, and a real, immediately-checked `npm ls -g` confirming nothing was installed globally, not a description of intended behavior. ## 1. Why This Even Matters — A Story First Borrowing a spec

Question 7

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 8

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 9

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 10

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

NODE.JSDECODED.

Easy

What are stream piping and the .pipe() method in Node.js?

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

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

Explain how modules work in Node.js.

What is the difference between string concatenation and path.join/path.resolve?

What is npx and how does it differ from a global install?

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

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

Medium

How would you implement caching in a Node.js application?

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

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

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

`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)?

How can you debug a Node.js application?

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

Hard

What is diagnostics_channel and when would you use it?

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

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

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

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

How do you secure your Node.js API endpoints?

How do you add OpenTelemetry distributed tracing to a Node.js service?

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