Question 1

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 2

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 3

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 4

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 5

What is the role of a bundler like Webpack in a React project?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes you have run a build. **Difficulty:** Easy to Medium > **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 running a real JSX file through this project own compiler toolchain, not copied from documentation. ## 1. Why This Even Matters — A Story First A publisher does not hand a reader a box of loose man

Question 6

What are React's design principles?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes broad familiarity with the API. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a discussion question rather than a mechanical one, so instead of a "Verified" section it cites the React team own published principles and ties each to a concrete API you already use. ## 1. Why This Even Matters — A Story First

Question 7

How do you handle memory leaks in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The listener counts in section 3 and the unmount behaviour in section 6 were produced by executing real mount and unmount cycles against React 19.2.8 in this repo. ## 1. Why This Even Matters — A Story First You rent a meeting room and book

Question 8

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

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes memo and hooks. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The render counts quoted below were measured on React 19.2.8 across this collection; see avoiding re-renders with composition and

Question 9

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

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes Context and hooks. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a judgement question, so it leans on the measured Context behaviour from why Context re-renders every consumer rather than introducing new measurements. ## 1. Why

Question 10

What are Higher-Order Components (HOCs) in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes components and props. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The losses documented in section 4 were produced by actually building a naive HOC on React 19.2.8 and inspecting what survived. ## 1. Why This Even Matters — A Story First Think of a gift-wrapping service. You hand over a boxed appliance and get back the

REACT.JSDECODED.

Easy

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

What are the advantages of using React over plain JavaScript?

How do you pass data between components in React?

How do you debug React applications?

What is the role of a bundler like Webpack in a React project?

Medium

What are React's design principles?

How do you handle memory leaks in React?

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

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

What are Higher-Order Components (HOCs) in React?

How do you optimize performance in a React application?

Hard

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

cache() and fetch memoization — request deduplication in RSC