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 difference between readFile and createReadStream in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic `fs` module familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The numbers below came from **actually reading a real 20MB file** both ways on Node v24.19.0, not a description of expected behavior. ## 1. Why This Even Matters — A Story First Moving a house's contents in one giant crate needs a crane

Question 4

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 5

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 6

What is the difference between blocking and non-blocking I/O in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `fs` module and event-loop familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The tick counts and timings below came from **actually running both versions** on Node v24.19.0 against a real 50MB file, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A single toll-booth work

Question 7

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 8

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 9

What is the purpose of the AbortController in modern Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `fetch`/Promise familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every cancellation below was **actually executed**, including a first attempt that failed for the wrong reason and was corrected before being reported — real timing, not a description. ## 1. Why This Even Matters — A Story First Ordering f

Question 10

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js tooling and package-management interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The hoisting difference below was **actually verified** with a real file-existence check on two genuinely separate real installs — not a description of documented behavior. ## 1. Why This Even Matters — A Story First A messy shared closet where anyone

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 difference between readFile and createReadStream in Node.js?

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

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

What is the difference between blocking and non-blocking I/O in Node.js?

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

What is the purpose of `dirname` and `filename` in Node.js?

Medium

What is the purpose of the AbortController in modern Node.js?

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

What are Node.js Streams and when would you use them?

What is the difference between an ORM, a query builder, and a raw driver?

How does the thread pool work in Node.js?

Describe the `Buffer` class in Node.js and its use cases.

What is the purpose of the 'zlib' module in Node.js?

Explain how to read and write large files using streams in Node.js

Hard

Describe the Node.js architecture.

What do `unref()` and `ref()` do on a Node.js Timeout, and why do timers drift?

How do you secure your Node.js API endpoints?

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