Question 1

How does 'use strict' change what `this` refers to inside a regular function called without a receiver, compared to non-strict mode?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript this-binding 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 — captured output, not illustrative sample text. ## 1. Why This Even Matters — A Story First Imagine handing someone a form that says "sign here as: ___" with the blank left empty. In a lenient office,

Question 2

What are modules in JavaScript?

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 module-caching claim below was actually run and confirmed inside a real CommonJS script. ## 1. Why This Even Matters — A Story First A shared office supply closet, restocked once at the start of the day, is used identically by every single department that visits it

Question 3

What is an IIFE?

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 scoping and immediate-execution claims below were actually run in Node. ## 1. Why This Even Matters — A Story First Think of a magician who steps behind a curtain, does some private setup work, and immediately steps back out — the audience never sees, and can never

Question 4

How do Import Attributes (`with { type: "json" }`) work and why did they replace import assertions?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript/modules interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The dynamic import below was actually executed against a real JSON file written to disk for this verification. ## 1. Why This Even Matters — A Story First Handing a customs officer a sealed package without a label used to mean the officer had to guess, or you had to separ

Question 5

What is the difference between ES modules and CommonJS?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript/Node.js fundamentals interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The caching and environment claims below were actually run in Node, directly inside a real CommonJS script. ## 1. Why This Even Matters — A Story First CommonJS's `require()` is like asking a librarian in person for a book by a title you might decide on the s

Question 6

What does 'use strict' do?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every sloppy-vs-strict contrast below was actually run in Node — not recited from documentation. ## 1. Why This Even Matters — A Story First Sloppy mode is like a lenient proofreader who quietly fixes your typos without telling you — convenient in the moment, but it

Question 7

How does top-level await change how an ES module and its importers load, and what are the risks of using it carelessly?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript module-system interviews. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every timestamp and error below is **real, captured output** — a live browser run, a real Node ESM run with actual millisecond timestamps, and a genuine crash reproduction — not illustrative sample output. ## 1. Why This Even Matters — A Story First A relay race where

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