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

What are React Developer Tools and how do you use them?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes you have built a React app. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The React 19 API surface referenced in section 6 was read off the installed React 19.2.8 in this repo. ## 1. Why This Even Matters — A Story First The browser Elements panel shows you the finished building: walls, doors, paint. What it cannot show yo

Question 3

What is the purpose of the `key` prop when rendering lists in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes rendering lists. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The mismatch in section 3 was produced by typing into a real input and then reordering the list on React 19.2.8. ## 1. Why This Even Matters — A Story First A cloakroom numbers its hooks rather than its coats. Hook 1, hook 2, hook 3. It works perfectl

Question 4

Explain the concept of 'lifting state up' in React.

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes props and state. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is the focused technique; passing data between components surveys all the mechanisms, and unidi

Question 5

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 6

How do you pass data between components in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes props and state basics. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The composition measurement referenced in section 6 was produced by counting real renders on React 19.2.8; see composition for the full figures. ## 1. Why This Ev

Question 7

What is JSX?

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes JavaScript basics, no React required. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The compiled output in section 3 was produced by actually running a JSX source file through this project bundler toolchain, and the escaping behaviour in section 5 by rendering it in React 19.2.8. ## 1. Why This Even Matters — A Story First M

Question 8

What is the difference between element and component in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes basic JSX familiarity. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every object-shape claim below was produced by inspecting real values in React 19.2.8, not described from documentation. ## 1. Why This Even Matters — A Story First A **recipe** for a cake is not a cake. It is also not an *order* for a cake. -

Question 9

What are fragments in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes basic JSX. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The DOM output in section 3 was produced by rendering both versions in React 19.2.8 and reading back the real HTML. ## 1. Why This Even Matters — A Story First You need to post three documents. The post office insists on one item, so you put them in an envelope. Fine

Question 10

What is the Virtual DOM in React?

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes basic components. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The reconciliation behaviour in section 5 was produced by actually swapping an element type on React 19.2.8 and observing what happened to the child state. ## 1. Why This Even Matters — A Story First An architect wants three changes to a building. They do not de

REACT.JSDECODED.

Easy

What are React Hooks? Name a few common ones.

What are React Developer Tools and how do you use them?

What is the purpose of the `key` prop when rendering lists in React?

Explain the concept of 'lifting state up' in React.

What are the advantages of using React over plain JavaScript?

How do you pass data between components in React?

What is JSX?

What is the difference between element and component in React?

Medium

What are React's design principles?

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

Describe the `useRef` hook and its typical use cases.

How does React handle security concerns like XSS?

useOptimistic — how do you build instant UI for Server Actions?

How would you structure a large React application?

What are render props and how do they work?

Explain the concept of 'composition' in React components.

Hard

What causes stale closures in React hooks, and how do you fix them correctly?

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

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

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

What problem does `useSyncExternalStore` solve?

How do you optimize React component rendering?

How do you avoid re-renders with composition instead of memoization?

What is `useDeferredValue` and how does it differ from debouncing?