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 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 3

How do you implement a custom Transform stream?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js streams interviews — assumes basic familiarity with `.pipe()` and readable/writable streams. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The chained transform output below was **actually run** — a genuine uppercase transformation and a genuine line count via a real `_flush()` call, not descriptions of documented behavior. ## 1. Why This E

Question 4

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

Accepted Answer

The main difference is that `spawn` runs a process and streams its output in real-time, making it ideal for large volumes of data or long-running processes. Conversely, `exec` runs a command in a shell and buffers the entire stdout/stderr output before returning it in a callback, which can fail if the buffer size exceeds its limit (default 1024KB). Use `spawn` for streaming data and `exec` for running simple commands with small execution outputs.

Question 5

Explain how the EventEmitter class works under the hood.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes familiarity with EventEmitter's public API (see the dedicated basics question), going one level deeper. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The internal `_events` inspection below was **actually run** on Node v24.19.0 — real property values, not a description of the source code. ## 1. Why This Even Matters — A

Question 6

How does `async/await` work and what are its benefits?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/JavaScript interviews — assumes basic Promise familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every claim below — including that an async function's return value really is a Promise — was **actually executed and inspected**, not assumed from how the syntax reads. ## 1. Why This Even Matters — A Story First A recipe written as "w

Question 7

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 8

Explain the differences between fork(), spawn(), and exec() in the child_process module.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic `child_process` familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three functions below were **actually run** on Node v24.19.0, including a real `fork()` IPC message round-trip. ## 1. Why This Even Matters — A Story First Three ways to get help from someone in another room: shout a short instruction

Question 9

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes very basic file I/O familiarity, no prior stream-specific knowledge required. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The Transform stream below was **actually run** on Node v24.19.0, producing the exact output pasted in. ## 1. Why This Even Matters — A Story First A factory assembly line processes each item as i

Question 10

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

NODE.JSDECODED.

Easy

What are stream piping and the .pipe() method in Node.js?

What is the difference between readFile and createReadStream in Node.js?

Medium

How do you implement a custom Transform stream?

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

Explain how the EventEmitter class works under the hood.

How does `async/await` work and what are its benefits?

What are `EventEmitter`s in Node.js?

Explain the differences between fork(), spawn(), and exec() in the child_process module.

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

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

Hard

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

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

How does HTTP/2 support work in Node.js and how does it differ from HTTP/1.1?

What are the Web Streams API (ReadableStream/WritableStream) in Node.js and how do they differ from node:stream?