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 does SharedArrayBuffer let two Web Workers share memory directly, and what race conditions do you need to guard against?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript concurrency / Web Worker interviews. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every number below is **real, measured output** — a genuine 4-worker race run and its Atomics-fixed counterpart, executed on this machine, plus a live check in a real (non-jsdom) browser tab — not illustrative sample numbers. ## 1. Why This Even Matters — A

Question 3

How would you transfer a large ArrayBuffer between a worker and the main thread without copying it, using postMessage's transfer list?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript Web Worker / performance interviews. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every number below is **real, measured output** — a live transfer executed in a real browser tab, and a real Node worker_threads timing comparison — not illustrative sample numbers. ## 1. Why This Even Matters — A Story First Mailing someone the actual ph

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Medium

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

Hard

How does SharedArrayBuffer let two Web Workers share memory directly, and what race conditions do you need to guard against?

How would you transfer a large ArrayBuffer between a worker and the main thread without copying it, using postMessage's transfer list?