Question 1

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 2

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 3

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 4

What are React Components?

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes JavaScript functions, no React required. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The instance and prototype claims in section 4 were produced by inspecting real components on React 19.2.8. ## 1. Why This Even Matters — A Story First Think about LEGO. A brick is small, does one thing, and — crucially — has a standard co

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

How does React handle security concerns like XSS?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes basic JSX. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every security behaviour below was produced by actually rendering the hostile input in React 19.2.8 and reading back the resulting DOM — including one result that contradicts a lot of older writing on this topic. ## 1. Why This Even Matters — A Story First A good l

Question 7

What are render props and how do they work?

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 memoisation measurement in section 5 was produced by counting real renders on React 19.2.8. ## 1. Why This Even Matters — A Story First A weather station measures temperature. It has no opinion about whether you want a number, a dial, or a chart — so inst

Question 8

How does React handle events?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes DOM event bubbling. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every ordering claim below was **executed against React 19.2.8** with real listeners attached alongside React ones; the raw output is in sections 3 and 5. For what the event object itself is, see

Question 9

Describe the benefits of using TypeScript with React.

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes basic TypeScript familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Section 3 is **five real compiler diagnostics**, produced by running the **TypeScript 7.0.2 installed in this repo** over a deliberately wrong component usage — exact codes and messages, not paraphrases. ## 1. Why This Even Matters — A Story First

Question 10

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

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes what React.memo is. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every render count and timing below was **executed against React 19.2.8** in a jsdom renderer; the raw output is in sections 3 and 6. This doc is the failure-mode companio

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