Question 1

What is `create-react-app` and when would you use it?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes you have started a React project before. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The deprecation status below was checked against the React team announcement rather than recalled — this is a topic where an out-of-date answer is very visible, so the source is cited inline. ## 1. Why This Even Matters — A Story First <

Question 2

What is the purpose of the cleanup function in useEffect?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect basics. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The exact call sequence in section 3 was produced by rendering a component through three dependency changes and an unmount on React 19.2.8. ## 1. Why This Even Matters — A Story First Every time you check into a hotel you get a key. Ever

Question 3

Describe the React component lifecycle.

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every ordering below is **executed output from React 19.2.8**, not a description — the raw sequences are in sections 3 and 5. ## 1. Why This Even Matters — A Story First A market stall has three moments: setting up before opening, adjusting through the day as st

Question 4

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

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every claim below was **executed against React 19.2.8** — the export check, the hook enumeration, the boundary catching a real error, and the setState merge behaviour. ## 1. Why This Even Matters — A Story First A workshop replaces its hand tools with powe

Question 5

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

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes effects and cleanup. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The counts in section 3 were **executed against React 19.2.8** by rendering the same component with and without StrictMode. **A production build was not measured here** — the development-only claim comes from the documented behaviour, and this do

Question 6

How do you safely handle async work and race conditions inside effects?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes effects and promises. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is the deep hazard taxonomy; handling async operations is the introduction, and the race-condition measurement quoted in section 3 comes from there. ## 1. Why This

Question 7

How did ref handling change in React 19 (ref as a prop, forwardRef, ref cleanup)?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes refs and forwardRef. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every claim below — including whether forwardRef warns — was produced by running the code on React 19.2.8 rather than read from a changelog. ## 1. Why This Even Matters — A Story First For years, handing a ref to a function compone

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