Question 1

What is globalThis?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The identity claim below was actually run in Node. ## 1. Why This Even Matters — A Story First Imagine three different countries calling the same building "City Hall," "Rathaus," and "Ayuntamiento" — the same physical building, three different local names, and any trav

Question 2

How do you implement a custom Promise.all polyfill?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript async/Promise interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result shown below is **real, captured output** from actually running the code in this doc on Node.js v24.19.0 — not illustrative sample output. ## 1. Why This Even Matters — A Story First Imagine ordering three packages online on the same day and ask

Question 3

How would you use the new Iterator helper methods (.map, .filter, .take, .drop) to process a large or infinite iterator lazily?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript iteration/collections interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every pull-count shown below is **real, captured output** from actually running the code in this doc on Node.js v24.19.0 — not illustrative sample output. ## 1. Why This Even Matters — A Story First Imagine a conveyor belt that makes an unlimited nu

Question 4

How do you implement a custom Promise.any polyfill?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript async/Promise interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result shown below is **real, captured output** from actually running the code in this doc on Node.js v24.19.0 — not illustrative sample output. ## 1. Why This Even Matters — A Story First Imagine calling five different pizza places at once and going

Question 5

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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Easy

What is globalThis?

Medium

How do you implement a custom Promise.all polyfill?

Hard

How would you use the new Iterator helper methods (.map, .filter, .take, .drop) to process a large or infinite iterator lazily?

How do you implement a custom Promise.any polyfill?

How do you implement a simple Promise library from scratch?