Question 1

What is the role of `react-dom`?

Accepted Answer

**Target Audience:** Frontend engineers preparing for React interviews — assumes basic familiarity with components. **Difficulty:** Easy to Medium > **How to read this doc:** Every concept is explained in plain language first. Right after, you will see a callout like 📌 Interview term: — that is the exact vocabulary a senior engineer would use for the same idea. Every package-export and behavioural claim below was produced by actually running React 19.2.8 in this repo, not describe

Question 2

What are the advantages of using React over plain JavaScript?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes JavaScript and DOM basics. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a trade-off question, so the answer below deliberately includes the costs — an interviewer is often testing whether you can argue against your own tool. ## 1. Why This Even Matters — A Story First Picture a whiteboard tracking a foot

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

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 5

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 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

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 8

What is `useFormStatus` in React 19, and why does it exist?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes Actions. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The measurement in section 3 was **executed against React 19.2.8** by calling the hook in two places at once during a real submission. Its sibling is

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

Question 10

React Compiler — how does auto-memoization work in React 19?

Accepted Answer

**Target Audience:** Frontend engineers preparing for senior React interviews — assumes familiarity with useMemo and React.memo. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The runtime inspection below was produced by reading the installed React 19.2.8 in this repo. Release-date and version claims were checked against the React team announcement rather than recalled —

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