Question 1

How do you enable gzip/Brotli compression for HTTP responses?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express performance interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real byte counts below are **actual, measured** raw wire bytes, captured via a client that bypasses automatic decompression specifically to measure what's genuinely sent — not illustrative numbers. ## 1. Why This Even Matters — A Story First Shipping a box stuf

Question 2

Explain the concept of 'middleware' in Express.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express interviews — assumes no prior Express-specific knowledge. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The chain-ordering and short-circuiting behavior below was **actually run** against a real Express server — genuine console output, not a description of intended behavior. ## 1. Why This Even Matters — A Story First An airport secu

Question 3

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 4

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 5

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 6

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 7

What is `npm` and what are its core functionalities?

Accepted Answer

npm stands for Node Package Manager. It is the default package manager for Node.js and is used for installing, sharing, and managing project dependencies. Its core functionalities include installing packages from the npm registry, managing project metadata in `package.json`, running scripts defined in `package.json`, and publishing your own packages to the registry. It's crucial for building and maintaining Node.js applications efficiently.

Question 8

How can you securely store and verify passwords in a Node.js application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js security-focused phone screens — assumes very basic hashing familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The hash/verify pair below was **actually run** on Node v24.19.0, using only Node's built-in `crypto` module — no external package installed. ## 1. Why This Even Matters — A Story First A safe-deposit box's combination is ne

Question 9

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 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

How do you enable gzip/Brotli compression for HTTP responses?

Explain the concept of 'middleware' in Express.js.

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

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

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

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

What is `npm` and what are its core functionalities?

How can you securely store and verify passwords in a Node.js application?

Medium

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

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

Explain the concept of 'event-driven architecture' in Node.js.

What are 'Event Emitting' patterns and how does error-first callback convention relate to them?

How do you implement a custom Transform stream?

What are Worker Threads in Node.js and when would you use them?

What is the difference between spawn() and exec() in Node.js?

What is the 12-factor app methodology as applied to Node.js services?

Hard

How do you profile CPU usage with --prof, 0x, or clinic.js flame graphs?

How do you handle circular dependencies in Node.js?

What is backpressure in Node.js streams and how do you handle it?

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

What is SSRF and how do you mitigate it in a Node.js backend?

How do you achieve concurrency in Node.js since it's single-threaded?

What are some common ways to improve performance in a Node.js application?

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