Question 1

What does queueMicrotask() do, and how does its callback ordering compare to a resolved Promise .then() and setTimeout(fn, 0)?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript event loop and async-ordering interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result below was actually run on Node.js v24.19.0 — the printed output is real, captured output, not illustrative sample text. ## 1. Why This Even Matters — A Story First Picture a barista mid-pour on a drink. Right next to the registe

Question 2

Explain the event loop, call stack, and task queues.

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript event loop and async-mechanics interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result below was actually run on Node.js v24.19.0 — the printed output is real, captured output, not illustrative sample text. This doc focuses on the MECHANICS (the call stack and how the loop drives the queues); for an exhaustive list

Question 3

What is the difference between microtasks and macrotasks?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript event loop and async-queue interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result below was actually run on Node.js v24.19.0 — the printed output is real, captured output, not illustrative sample text. This doc focuses on MEMBERSHIP -- an exhaustive list of what actually lives in each queue; for the underlying cal

Question 4

How do you implement a simple Promise library from scratch?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript async/Promise interview questions. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every test result shown below is **real, captured output** from actually running this doc's MyPromise implementation on Node.js v24.19.0 through 10 real test groups, including a direct interleaved comparison against native Promise — not illustrative sample outp

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Medium

What does queueMicrotask() do, and how does its callback ordering compare to a resolved Promise .then() and setTimeout(fn, 0)?

Hard

Explain the event loop, call stack, and task queues.

What is the difference between microtasks and macrotasks?

How do you implement a simple Promise library from scratch?