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 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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

What is React and its main features?

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes no prior React knowledge. **Difficulty:** Easy > **How to read this doc:** Every concept is explained in plain language first. Right after, you will see a callout like 📌 Interview term: — the exact vocabulary an interviewer expects. The object-shape claims below were produced by running React 19.2.8 in this repo. ## 1. Why This Even Matters — A Story First Imagine decorating a room by giving instructions over

REACT.JSDECODED.

Easy

What are React Hooks? Name a few common ones.

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

How do you handle side effects in functional components?

What is the role of `react-dom`?

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

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?

Medium

What are React's design principles?

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

How would you structure a large React application?

What are render props and how do they work?

Describe the React component lifecycle.

Explain the concept of 'composition' in React components.

How does React handle events?

How do you handle asynchronous operations in React functional components?

Hard

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

How do Suspense data-fetching waterfalls happen, and how do you avoid them?

What is server-side rendering (SSR) and when would you use it with React?

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

React Server Components vs SSR — what is the real difference?

When and why do you use `forwardRef` with `useImperativeHandle`?

Why does updating Context re-render all its consumers, and how do you fix it?

What does the `use()` hook do, and why is it special?