Question 1

What is the difference between useMemo and useCallback?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks and re-renders. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The recompute and identity counts in section 3 were measured across three real renders on React 19.2.8. ## 1. Why This Even Matters — A Story First Two different things get cached in a kitchen. The **stock** — simmered for hours — is made once and kept,

Question 2

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 3

How do you optimize performance in a React application?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes broad React familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a breadth question, so it leans on measurements taken elsewhere in this collection rather than introducing new ones — the render-cost figures come from preventi

Question 4

What is `React.memo` and when would you use it?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes props and re-render basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every render count below was measured by actually mounting the components and re-rendering their parent on React 19.2.8. ## 1. Why This Even Matters — A Story First A translator is handed a document and asked to translate it. Then handed it again.

Question 5

How do you optimize React component rendering?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes profiling basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The durations in section 3 were measured with React's own Profiler component on React 19.2.8. This doc is about **cost per render**; preventing unnecessary r

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Medium

What is the difference between useMemo and useCallback?

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

How do you optimize performance in a React application?

What is `React.memo` and when would you use it?

Hard

How do you optimize React component rendering?