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

How would you use Object.groupBy() to group an array of orders by status, and how does it compare to a manual reduce()?

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 claim below was actually run — both implementations were executed against the identical real orders array and their outputs directly compared. ## 1. Why This Even Matters — A Story First Sorting a pile of mail into labeled bins by recipient is a task every office

Question 3

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 4

What is the difference between localStorage, sessionStorage, and cookies?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript/browser-storage interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every storage claim below was actually run with jsdom's real storage implementations. ## 1. Why This Even Matters — A Story First `localStorage` is like a filing cabinet bolted to the building itself — every visitor, on every visit, sees the exact same shared cabine

Question 5

What is JSON and why is it commonly used?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals and data-interchange 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 Imagine shipping a package overseas. A JS backend, a Python se

Question 6

How do you implement infinite currying in JavaScript?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript closures and functional-programming 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 Think of a vending machine that keeps a running tab open: each coin you insert (each f

Question 7

How does the fetch API work?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript/browser-API interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every request below was actually made against a real local HTTP server spun up for this verification, not simulated. ## 1. Why This Even Matters — A Story First Calling a delivery company to ask "did my package arrive?" — the phone call itself succeeding (someone answ

Question 8

What is memoization?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals / performance interview questions. **Difficulty:** Easy-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 student working through a long worksheet of math pro

Question 9

What does Object.create do?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript prototype-system interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The prototype-less object's real thrown error, and the real, direct `__proto__`-key comparison below, were **actually run** — not descriptions of documented behavior. ## 1. Why This Even Matters — A Story First A brand-new employee with zero inherited company pol

Question 10

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

JAVASCRIPTDECODED.

Easy

What are template literals?

How would you use Object.groupBy() to group an array of orders by status, and how does it compare to a manual reduce()?

What is the difference between null and undefined?

What is the difference between localStorage, sessionStorage, and cookies?

What is JSON and why is it commonly used?

Medium

How do you implement infinite currying in JavaScript?

How does the fetch API work?

What is memoization?

What does Object.create do?

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

How do you deep clone an object in JavaScript?

How do you make an AJAX request?

What are private class fields?

Hard

What are Symbols and what are they used for?