Question 1

How do you manage component-level state without `useState` or `useReducer`?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks basics. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The class-component behaviour in section 3 was verified by rendering and clicking one on React 19.2.8 — worth checking rather than assuming, given how much has been removed from React 19. ## 1. Why This Even Matters — A Story First A kitchen has a whiteb

Question 2

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 3

Explain the concept of 'composition' in React components.

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes props and components. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The render counts in section 4 were produced by actually counting renders on React 19.2.8 in this repo — this is the part of the answer that most candidates only assert. ## 1. Why This Even Matters — A Story First Consider two ways to build a range of co

Question 4

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

Question 5

When and why do you use `forwardRef` with `useImperativeHandle`?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes refs basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The property counts and the React 19 ref behaviour in sections 3 and 5 were **executed against React 19.2.8**. Related: how ref handling changed in React 19. ## 1. Why This Even Matt

Question 6

Why must React state updates be immutable?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes state basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The render counts and the delayed corruption in section 3 were produced by actually mutating state on React 19.2.8. ## 1. Why This Even Matters — A Story First A librarian checks whether a shelf has changed by looking at the label on its end, not by reading

Question 7

Compare render-as-you-fetch, fetch-on-render, and fetch-then-render.

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes Suspense basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three patterns in section 3 were **executed against React 19.2.8** with the same two 120ms requests, and the timings are the measured ones. Related: Suspense waterfal

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