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

createContext vs use(Context) — new context consumption in React 19

Accepted Answer

# `createContext` vs. `use(Context)`: New Context Consumption in React 19

**Target Audience:** Frontend engineers preparing for React interviews — assumes basic familiarity with Context and Hooks.
**Difficulty:** Medium

> **How to read this doc:** Every concept is explained in plain language first. Right after, you'll see a callout like `📌 Interview term:` — that's the exact vocabulary a senior engineer would use for the same idea.

## 1. Why This Even Matters — A Story First

Think of Contex

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

How do you debug React applications?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks and component basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The React 19 debugging API named in section 5 was read off the installed React 19.2.8 in this repo rather than recalled. ## 1. Why This Even Matters — A Story First A doctor presented with "I feel unwell" does not start by ordering every test in th

Question 8

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 9

The `use()` API with Suspense — how do you unwrap promises in render?

Accepted Answer

`use()` is a React 19 primitive that unwraps a Promise or Context during render.

Question 10

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

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes props and state. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The default-value and re-render behaviour below were measured on React 19.2.8. This doc covers *what Context is and when to use it*; why it re-renders every consumer covers

REACT.JSDECODED.

Easy

What are React Hooks? Name a few common ones.

createContext vs use(Context) — new context consumption in React 19

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.

How do you debug React applications?

Medium

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

The `use()` API with Suspense — how do you unwrap promises in render?

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

What is the difference between useMemo and useCallback?

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

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

What is 'prop drilling' and how can it be avoided?

How do you manage global state in a large React application?

Hard

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

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

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

Why must React state updates be immutable?

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

When does `React.memo` do nothing — or actually hurt performance?

How does automatic batching work in React 18, and how do you opt out?

What changed with Context in React 19 (`<Context>` as a provider)?