Question 1

What are template literals?

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 interpolation and newline-preservation claims below were actually run in Node. ## 1. Why This Even Matters — A Story First Writing a paragraph by hand with a regular quoted string is like typing a letter where every single line break has to be manually spelled out

Question 2

What is the difference between var, let, and const?

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:. Every scoping and TDZ claim below was actually run in Node — including the classic loop-closure bug. ## 1. Why This Even Matters — A Story First Imagine a shared office whiteboard (`var`) versus a sticky note stuck to one specific desk (`let`/`const`). Anyone in the wh

Question 3

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 4

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 5

What is the difference between preventDefault and stopPropagation?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript DOM/events interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both isolated tests below were actually run with jsdom. ## 1. Why This Even Matters — A Story First Imagine a letter mailed through a chain of post offices, each one an ancestor listener along the route. `stopPropagation()` is telling the current post office "do not fo

Question 6

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 7

What is the difference between null and undefined?

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:. Every check below was actually run in Node. ## 1. Why This Even Matters — A Story First Think of a form field on a job application. A field that was never shown to the applicant at all is like `undefined` — nobody had the chance to fill it in. A field that was shown, a

Question 8

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 9

What are the quirks of the typeof operator?

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:. Every result below, including the real thrown error, was actually run in Node. ## 1. Why This Even Matters — A Story First Asking "does this specific book exist anywhere in the library?" is a genuinely safe question to ask even if the book's title was never catalogued

Question 10

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

JAVASCRIPTDECODED.

Easy

What are template literals?

What is the difference between var, let, and const?

What is hoisting in JavaScript?

Describe the concept of 'scope' in JavaScript.

What is the difference between preventDefault and stopPropagation?

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

What is the difference between null and undefined?

What is globalThis?

Medium

Debounce vs throttle — implement debounce

How do you implement infinite currying in JavaScript?

Explain 'this' keyword in JavaScript.

How would you write a Proxy 'set' trap that validates a value before allowing an assignment, and what happens if you return false?

What are modules in JavaScript?

What is lexical scoping and the scope chain?

What is an IIFE?

How would you remove an item from an array immutably using toSpliced(), and how does it compare to splice()?

Hard

What does yield* do in a generator?

What are async iterators and for await...of?

How do you implement a throttle function?

What is the temporal dead zone?

How does the Temporal API fix JavaScript Date — Instant, PlainDate and ZonedDateTime?

How would you implement a curry() function that supports partial application with placeholder arguments?