Question 1

How would you use the BroadcastChannel API to sync application state across multiple open browser tabs?

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 claim below — including the self-exclusion behavior — was verified live in a real, current browser via the Claude Browser pane. `BroadcastChannel` is confirmed genuinely NOT implemented in jsdom. ## 1. Why This Even Matters — A Story First A group text message

Question 2

How do you implement a deepFreeze function recursively?

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 claim below — including the cycle-safety behavior — was actually run, not just reasoned about. ## 1. Why This Even Matters — A Story First Locking the front door of a house but leaving every internal room door wide open and unlocked technically means "the house

Question 3

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

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 claim below was actually run — the "original untouched" claim specifically was verified by logging the SAME original array variable both before and after the `toSpliced()` call. ## 1. Why This Even Matters — A Story First Editing a shared document by literally

Question 4

How would you combine multiple AbortSignals or add a timeout to a fetch request using AbortSignal.any() and AbortSignal.timeout()?

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 claim below — including which signal genuinely wins each race — was actually run and timed against a real network endpoint. ## 1. Why This Even Matters — A Story First A race with two separate finish-line judges — one who blows a whistle if a runner crosses the

Question 5

What does `Promise.try()` do and why is it better than `Promise.resolve().then(fn)`?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript/async interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every throw and catch path below was actually run in Node. ## 1. Why This Even Matters — A Story First Calling a function directly and hoping any error gets funneled into a `.catch()` somewhere downstream is like shouting a warning INTO a mailbox and hoping the mail carrier

Question 6

How would you use Reflect.ownKeys() inside a Proxy to correctly enumerate both string and symbol keys, including non-enumerable ones?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript metaprogramming (Proxy/Reflect) interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every ordering and error message shown below is **real, captured output** from actually running the code in this doc on Node.js v24.19.0 — not illustrative sample output. ## 1. Why This Even Matters — A Story First Imagine asking someone t

Question 7

What is the Reflect API?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript meta-programming interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The real boolean-return proof, the real combined-keys result, and the real constructor call below were **actually run** — not descriptions of documented behavior. See also this bank's own dedicated

Question 8

How would you write a deep-clone function that correctly handles a self-referencing (circular) object without infinite recursion?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript object-manipulation interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result shown below is **real, captured output** from actually running the code in this doc on Node.js v24.19.0 — not illustrative sample output. ## 1. Why This Even Matters — A Story First Imagine photocopying a family tree poster where, somewhe

Question 9

What is a Proxy in JavaScript?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript meta-programming interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every trap firing and the real virtualized property below were **actually run** — not descriptions of documented behavior. See also this bank's dedicated Proxy get-trap and

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