Question 1

What is hoisting in JavaScript?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals interview questions. **Difficulty:** Easy > **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 Think of a scope like a conference room with name tags laid out before the meeting

Question 2

Describe the concept of 'scope' in JavaScript.

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals interview questions. **Difficulty:** Easy > **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 program as rooms inside rooms: a house (global scope) contains a kitchen

Question 3

What are `let`, `const`, and `var`? What are their differences?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals interview questions. **Difficulty:** Easy > **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 Think of three different ways to reserve a locker. `var` reserves a locker for the

Question 4

How does Array.prototype.toReversed() avoid the classic bug of accidentally mutating a shared array reference?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript array-methods interview questions. **Difficulty:** Easy > **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 two people each holding what they believe is their own copy of the same shopping list, but it is actua

Question 5

What is destructuring?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript ES6+ syntax interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real swap, the real nested/renamed/defaulted extraction, and the real thrown error on `null` below were **actually run** — not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First Unpacking a delivered grocery bag by reaching in and pulli

Question 6

Explain 'this' keyword in JavaScript.

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals 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 covers the CONCEPT of this (why it behaves the way it does); for the exact binding-rule priority order with verified o

Question 7

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 8

What is lexical scoping and the scope chain?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals 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 covers the GENERAL rule for how any variable lookup resolves in JavaScript; for the specific case where a function out

Question 9

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 10

What are closures in JavaScript?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals 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 covers closures specifically (a function retaining access to its outer scope); for the more general rule that governs

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