Question 1

What are React Hooks? Name a few common ones.

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes components and props. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The hook inventory in section 4 was read directly off the installed React 19.2.8 rather than recalled, which matters because several were added recently. ## 1. Why This Even Matters — A Story First Imagine a workshop where only the master craftsmen were allo

Question 2

How do you manage component-level state without `useState` or `useReducer`?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks basics. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The class-component behaviour in section 3 was verified by rendering and clicking one on React 19.2.8 — worth checking rather than assuming, given how much has been removed from React 19. ## 1. Why This Even Matters — A Story First A kitchen has a whiteb

Question 3

What is the difference between `useState` and `useReducer`?

Accepted Answer

**Target Audience:** Frontend engineers preparing for React interviews — assumes familiarity with useState. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term: — the exact vocabulary an interviewer expects. Every behavioural claim below was produced by actually running React 19.2.8 in this repo, including the render counts. ## 1. Why This Even Matters — A Story First Imagine a shop wit

Question 4

What is the purpose of the `deps` array in `useEffect` and `useCallback`?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every count in sections 3 and 5 was measured by rendering the components three times on React 19.2.8 and recording how often each hook actually ran. ## 1. Why This Even Matters — A Story First A courier is told: "redeliver whenever the address c

Question 5

How do you test React components?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes basic testing familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Section 3 is **executed** — the same three assertions run against a component and against a **pure refactor** of it, using the Testing Library version installed in this repo. ## 1. Why This Even Matters — A Story First A restaurant inspector could g

Question 6

What are React custom hooks and when should you use them?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useState and useEffect. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The state-independence result in section 3 was produced by mounting two components that use the same hook and clicking one of them on React 19.2.8. ## 1. Why This Even Matters — A Story First A recipe for bread is not a loaf o

Question 7

When would you choose a class component over a functional component with hooks?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every claim below was **executed against React 19.2.8** — the export check, the hook enumeration, the boundary catching a real error, and the setState merge behaviour. ## 1. Why This Even Matters — A Story First A workshop replaces its hand tools with powe

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

Question 10

Why does React 18 StrictMode double-invoke your components and effects?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes effects and cleanup. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The counts in section 3 were **executed against React 19.2.8** by rendering the same component with and without StrictMode. **A production build was not measured here** — the development-only claim comes from the documented behaviour, and this do

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Easy