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 do you handle side effects in functional components?

Accepted Answer

**Target Audience:** Frontend engineers preparing for React interviews — assumes basic familiarity with Hooks. **Difficulty:** Medium > **How to read this doc:** Every concept is explained in plain language first, then tagged with 📌 Interview term: — the exact vocabulary an interviewer expects. Every ordering and lifecycle claim below was produced by actually running React 19.2.8 in a real DOM (jsdom) in this repo, not described from documentation. ## 1. Why This Even Matters — A

Question 3

Explain the concept of 'unidirectional data flow' in React.

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes props and state. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The prop-mutation result in section 4 was produced by actually assigning to a prop on React 19.2.8 and catching what happened. ## 1. Why This Even Matters — A Story First A newspaper has one editor per section. Reporters file copy upward; the editor decides what

Question 4

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 5

How do you handle asynchronous operations in React functional components?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect and promises. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The race-condition outcome in section 4 and React warning text in section 3 were both produced by running the code on React 19.2.8, not described from memory. ## 1. Why This Even Matters — A Story First You order a taxi, change your mind,

Question 6

How do you handle forms in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes state and events. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The FormData and useActionState results below were produced by submitting real forms on React 19.2.8. ## 1. Why This Even Matters — A Story First Two ways to take an order in a restaurant. The waiter can write each item down as you

Question 7

What are Effect Events (`useEffectEvent`) and what problem do they solve?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes effects and dependency arrays. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The re-run counts in section 3 were measured on React 19.2.8, where useEffectEvent is a stable export. ## 1. Why This Even Matters — A Story First A courier is told to redeliver whenever the **address** changes. Sensible. They

Question 8

What are Portals in React and when would you use them?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes JSX and event basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The DOM placement and the event ordering in sections 3 and 4 were **executed against React 19.2.8**. Related: how React handles events, which explains why the bubbling work

Question 9

useEffectEvent — separating reactive and non-reactive logic in Effects

Accepted Answer

`useEffectEvent` (React 19 experimental, now `useEffectEvent`) creates a non-reactive callback that always sees the latest props/state but never appears in effect deps.

Question 10

When would you use `useLayoutEffect` instead of `useEffect`?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The ordering in section 3 was measured on React 19.2.8. **One honest limit:** jsdom does not paint, so the *flicker* this hook prevents cannot be demonstrated in a unit environment — the ordering and DOM-mutation timing were verified, and the visual conseq

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Easy