Question 1

What is the difference between dependencies, devDependencies, and peerDependencies?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — assumes basic npm familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The install behavior below came from **actually running** `npm install --save-dev` and a subsequent `npm install --omit=dev` on this machine, not a description of expected behavior. ## 1. Why This Even Matters — A Story First A moving company packs t

Question 2

What is Node.js and why is it popular?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js phone screens — no prior Node knowledge assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The version numbers below were read directly from a running Node process on this machine, not quoted from memory. ## 1. Why This Even Matters — A Story First Before Node.js, JavaScript lived almost entirely in one place: the browser, running whatev

Question 3

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes `EventEmitter` basics from its own dedicated question. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The subscriber-addition demonstration below was **actually run** on Node v24.19.0 — the fourth subscriber genuinely started receiving events with zero changes to the publisher, not a description of expected

Question 4

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with Node's concurrency model (see the dedicated question). **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a judgment-and-trade-off question; the technical claims it rests on are grounded in real measurements verified in their own dedicated questions, cited here rather than re-derived. #

Question 5

What are some best practices for structuring a Node.js project?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the dependency-injection question's real, verified demonstration. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a structural/organizational judgment question; the technical claim it rests on (that layered structure enables real dependency injection) is grounded in the real, verified

Question 6

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design and deployment-practices interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The config demo below was **actually run twice**, with and without environment variables set — real, different output, not a description of intended behavior. ## 1. Why This Even Matters — A Story First A recipe that says "add the amount of sal

Question 7

How does Node.js handle multi-threading behind the scenes if JavaScript is single-threaded?

Accepted Answer

While the JavaScript execution engine (V8) runs on a single thread, Node.js offloads heavy asynchronous operations to C++ APIs and libuv. Libuv maintains a thread pool (default size of 4) to execute blocking tasks like cryptography, compression, and file system I/O in parallel. Once a background thread finishes a task, it notifies the main thread to execute its callback via the event loop queue.

Question 8

What are `EventEmitter`s in Node.js?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes very basic callback familiarity, no prior EventEmitter knowledge required. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every behavior below was **actually executed** on Node v24.19.0, including the special `'error'`-event case, verified as a real thrown and caught exception. ## 1. Why This Even Matters — A Story First

Question 9

What is the Repository pattern and how does it decouple business logic from the database?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js architecture and testing interviews — assumes familiarity with the unit-vs-integration-testing question's real speed-comparison proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The identical business logic running against two real, different backing stores below was **actually executed** — real, correct output from both, plus a real sour

Question 10

Explain the Node.js event loop.

Accepted Answer

The **event loop** is the heart of Node's concurrency: a single thread that repeatedly runs queued callbacks across ordered **phases** (timers → pending → poll → check → close). Between phases (and after each callback) it drains the **microtask** queues (process.nextTick, then Promises). This lets one thread juggle many async operations without blocking.

NODE.JSDECODED.

Easy

What is the difference between dependencies, devDependencies, and peerDependencies?

What is Node.js and why is it popular?

Medium

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

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

What are some best practices for structuring a Node.js project?

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

How does Node.js handle multi-threading behind the scenes if JavaScript is single-threaded?

What are `EventEmitter`s in Node.js?

What is the Repository pattern and how does it decouple business logic from the database?

Explain the Node.js event loop.

Hard

How do you handle circular dependencies in Node.js?

How do you implement microservices communication in Node.js?

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

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

Describe the Node.js architecture.

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