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 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 3

What are optional chaining and nullish coalescing?

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 throw-vs-no-throw and call-count claim below was actually run in Node. ## 1. Why This Even Matters — A Story First Walking down a hallway of doors, checking behind each one for a specific box: optional chaining is like a careful walker who, upon finding any door

Question 4

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 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

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 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

How do you handle asynchronous operations in JavaScript?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript fundamentals/async interviews. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three approaches below were actually run against the identical real delayed operation. ## 1. Why This Even Matters — A Story First Ordering food can be described three different ways in English — "call me when it's ready," "I'll check back with you and you'll

Question 9

What are the spread and rest operators?

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 shallow-copy proof, the real iterable-spread demonstration, and the real rest-parameter-position error below were **actually run** — not descriptions of documented behavior. See also this bank's own dedicated

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

What are optional chaining and nullish coalescing?

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

What is destructuring?

What is JSON and why is it commonly used?

Medium

What are modules in JavaScript?

How do you handle asynchronous operations in JavaScript?

What are the spread and rest operators?

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

What is the difference between arrow and regular functions?

What are the basics of regular expressions in JavaScript?

How do getters and setters work?

What are private class fields?

Hard

What does the RegExp `v` flag (Unicode Sets) add over the `u` flag?

Why can pushing a single non-numeric value into a large numeric array tank its performance in V8, and how would you avoid it?

How would you make a custom class iterable with for...of by implementing Symbol.iterator as a generator method?

What is the Reflect API?

What are Symbols and what are they used for?

Explain how prototypal inheritance differs from classical inheritance.

How do Stage 3 JavaScript Decorators work — class, method and field decorators?

What is ShadowRealm and how does it provide true JavaScript sandboxing?