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

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 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

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 6

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 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

forwardRef removal — how do refs work as props in React 19?

Accepted Answer

In React 19 `ref` is a normal prop. Function components receive `ref` like any other prop, so `forwardRef` is no longer needed and is deprecated.

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?

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

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

How do you pass data between components in React?

Explain the concept of 'unidirectional data flow' in React.

What is JSX?

What is the difference between element and component in React?

Medium

What are render props and how do they work?

Explain the concept of reconciliation in React.

Describe the React component lifecycle.

Explain the concept of 'composition' in React components.

What is the Context API in React and when would you use it?

RSC vs Client Components — when do you add 'use client' in Next.js 15?

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

How do you prevent unnecessary re-renders in functional components?

Hard

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

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

How do you optimize React component rendering?

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

What are Portals in React and when would you use them?

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

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

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