Question 1

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 2

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 3

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 4

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 5

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

Question 6

How do you handle forms in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes state and events. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The FormData and useActionState results below were produced by submitting real forms on React 19.2.8. ## 1. Why This Even Matters — A Story First Two ways to take an order in a restaurant. The waiter can write each item down as you

Question 7

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

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 re-render figures quoted in section 4 were measured on React 19.2.8; see avoiding re-renders with composition for the full run. ## 1. Why This Even Matters — A

Question 8

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

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