Question 1

What are React synthetic events?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — no prior knowledge of the event system assumed. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Everything about the event object below was **executed against React 19.2.8** and the raw output is pasted in section 3. For the delivery mechanism — where the listener actually lives — see

Question 2

How does React handle events?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes DOM event bubbling. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every ordering claim below was **executed against React 19.2.8** with real listeners attached alongside React ones; the raw output is in sections 3 and 5. For what the event object itself is, see

Question 3

How do you manage global state in a large React application?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes Context and hooks. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a judgement question, so it leans on the measured Context behaviour from why Context re-renders every consumer rather than introducing new measurements. ## 1. Why

Question 4

How do you optimize performance in a React application?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes broad React familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a breadth question, so it leans on measurements taken elsewhere in this collection rather than introducing new ones — the render-cost figures come from preventi

Question 5

How does `useOptimistic` enable optimistic UI in React 19?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes transitions and actions. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The timing behaviour in section 3 was produced by clicking a real button on React 19.2.8 and reading the DOM before and after the action resolved. ## 1. Why This Even Matters — A Story First A bartender takes your order and puts a glass on the co

Question 6

What causes hydration mismatches, and how do you handle them?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes what hydration is. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Section 3 is **four mismatches actually triggered against React 19.2.8**, with the recoverable-error count, the console warnings and the winning value recorded for each. The

Question 7

Partial Prerendering (PPR) in Next.js 15 — static shell + dynamic holes

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes SSR and Suspense. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** PPR is a Next.js build-and-serve feature and **cannot be executed in this environment** — there is no Next.js runtime here. Everything below is stated from the documented model rather than measured, and this doc says so rather

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