Question 1

What is `PropTypes` and when would you use it?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes basic component knowledge. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This topic has a genuine breaking change behind it, so the central claim below was verified by actually rendering a component with propTypes on React 19.2.8 and by checking the React upgrade guide — not recalled. ## 1. Why This Even Matter

Question 2

How do you fetch data in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This doc is the decision landscape; async operations covers the mechanics and race conditions, and

Question 3

What is the difference between controlled and uncontrolled components?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — no prior forms knowledge assumed. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The warning texts and the ref reading in sections 4 and 5 were **captured by executing against React 19.2.8**, not quoted from memory. Related: Actions in React 19, which ch

Question 4

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 5

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 6

useFormStatus & useActionState — modern form handling in React 19

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes Actions. **Difficulty:** Medium > **How to read this doc:** this is the **practical assembly** doc. The mechanics of each hook live in useActionState and useFormStatus; here

Question 7

Server Actions — how do mutations work without API routes in Next.js 15?

Accepted Answer

**Target Audience:** Engineers preparing for Next.js interviews — assumes what the directive does. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** this needs a running Next.js server and there is none here, so the workflow was **not executed**. The React-level pieces it builds

Question 8

What are Actions in React 19, and how do they change form handling?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes forms and hooks basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every behaviour below was **executed against React 19.2.8** by rendering a form into jsdom and submitting it; the raw output is in sections 3 and 5. The focused companions are

Question 9

What does the `useActionState` hook do in React 19?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes what Actions are. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The tuple shape and the render sequence in section 3 were **executed against React 19.2.8** by submitting a real form in jsdom. Its sibling is

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