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 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

How do you handle CORS (Cross-Origin Resource Sharing) in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express and web-security interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The header behavior below was **actually observed** from a real running Express server with the real `cors` middleware — genuine response headers, not a description of intended behavior. ## 1. Why This Even Matters — A Story First A nightclub bouncer checks

Question 4

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 5

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 6

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 7

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 8

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 9

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 10

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

NODE.JSDECODED.

Easy

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

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

How do you handle CORS (Cross-Origin Resource Sharing) in Node.js?

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

Explain how modules work in Node.js.

Medium

How does the Node.js event loop work?

What is AbortSignal.timeout and how do you cancel async work cleanly?

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 is CSRF and how do you protect a Node.js API against it?

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

When would you choose Node.js over other backend technologies?

Hard

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

How do you handle circular dependencies in Node.js?

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

What is a ReDoS (Regular Expression Denial of Service) attack and how do you avoid it?

What is diagnostics_channel and when would you use it?

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

How do you implement a circuit breaker for unreliable downstream services?

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