Question 1

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 2

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 3

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 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

How do you monitor a Node.js application's memory usage in production?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js production-operations and system-design interviews — assumes familiarity with the memory-leaks question's real growth-pattern proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The memory numbers below are **real, captured output** from `node --expose-gc` on this machine — not illustrative placeholder numbers. ## 1. Why This Even Matters

Question 6

What is the perf_hooks module and how do you measure performance?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js performance-measurement interviews — assumes familiarity with the CPU-profiling question's real hot-function identification. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The cross-validated timing below is **real, measured** output — two genuinely independent measurement mechanisms agreeing closely on the actual real duration, not illustrat

Question 7

Explain how clustering works in Node.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the single-thread concurrency model 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 multi-PID result below was **actually observed** from a real `cluster.fork()` setup on Node v24.19.0 — real, distinct process IDs, not a description of load balancing. ##

Question 8

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js performance-diagnostics interviews. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The profiling output below is **real, actual output** from running `node --prof` and `node --prof-process` against a genuine CPU-bound script on this machine — not illustrative sample output. ## 1. Why This Even Matters — A Story First A doctor diagnosing chest

Question 9

Explain how memory management and Garbage Collection work in the V8 engine.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic garbage-collection familiarity, no prior V8-internals knowledge required. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The GC log below is a **real, unedited excerpt** from actually running `node --trace-gc` against a real allocation loop on Node v24.19.0. ## 1. Why This Even Matters — A Story First A busy commerc

Question 10

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

Accepted Answer

**Target Audience:** Engineers preparing for Node.js interviews — assumes basic garbage-collection familiarity. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every memory number below came from **actually running the allocation and reading `process.memoryUsage()`** on Node v24.19.0, not an estimate. ## 1. Why This Even Matters — A Story First A warehouse never runs out of space because items g

NODE.JSDECODED.

Easy

What is Node.js and why is it popular?

What is the role of the V8 JavaScript engine in Node.js?

Medium

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

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

How do you monitor a Node.js application's memory usage in production?

What is the perf_hooks module and how do you measure performance?

Explain how clustering works in Node.js.

Hard

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

Explain how memory management and Garbage Collection work in the V8 engine.

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

Describe the Node.js architecture.

What is the 'vm' (Virtual Machine) module and when would you use it?

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

How do you capture and analyze a heap snapshot to find a memory leak?