Question 1

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 2

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 3

How does the Node.js event loop work?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic async/callback familiarity, no prior event-loop knowledge required. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every ordering claim below was **actually executed** on Node v24.19.0 — the exact console output is pasted in, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A sin

Question 4

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the event loop and the libuv thread pool from their own dedicated questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the blocking main-thread run and the Worker Thread run below used the **identical** computation, executed for real on Node v24.19.0 — the heartbeat contrast is mea

Question 5

How do you manage sessions and authentication in a Node.js web application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js authentication and system-design interviews — assumes familiarity with the 12-factor app question's real stateless-processes proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the session revocation and the JWT tamper-detection below were **actually run** — a real 401 after a real logout, and a real signature-check rejection of a genu

Question 6

How does Node.js handle crypto operations efficiently without blocking the event loop?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic event-loop and thread-pool familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the frozen and the free heartbeat below were **actually measured** on Node v24.19.0, using the identical computation in both cases. ## 1. Why This Even Matters — A Story First A single cashier who personally walks to a back

Question 7

Explain how the 'crypto' module secures sensitive data in Node.js

Accepted Answer

**Target Audience:** Engineers preparing for Node.js security-focused interviews — assumes basic hashing/encryption vocabulary. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the successful decryption and the tamper-rejection below were **actually run** on Node v24.19.0 — a real thrown authentication error, not a description of what should happen. ## 1. Why This Even Matters — A Story Fir

Question 8

How does the thread pool work in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic event-loop familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every timing number below came from **actually running real `crypto.pbkdf2` calls** on Node v24.19.0, not an estimate. ## 1. Why This Even Matters — A Story First A small kitchen with exactly four stovetop burners can cook four dishes simultane

Question 9

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes very basic binary-data familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The copy-vs-view distinction below was **actually verified** on Node v24.19.0 — a real mutation, and a real observed effect (or lack of one), not a description of expected behavior. ## 1. Why This Even Matters — A Story First A photocopy

Question 10

What are some common security best practices in Node.js applications?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js security-focused system-design interviews — assumes familiarity with the individual topics this answer cross-links to. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The `npm audit` and `helmet` results below came from **actually running both** against a real, deliberately-vulnerable setup on Node v24.19.0. ## 1. Why This Even Matters — A St

NODE.JSDECODED.

Easy

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

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

Medium

How does the Node.js event loop work?

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

How do you manage sessions and authentication in a Node.js web application?

How does Node.js handle crypto operations efficiently without blocking the event loop?

Explain how the 'crypto' module secures sensitive data in Node.js

How does the thread pool work in Node.js?

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

What are some common security best practices in Node.js applications?

Hard

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

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

Explain the concept of 'Event Loop Pollution' and how to avoid it.

Describe the Node.js architecture.

What is the role of `libuv` in Node.js?