React ⚡ Recently updatedUpdated on Jun 30, 2026 — this content may still be evolving.

React: Mock Interview (45 Minutes)

Practice with a friend. Switch roles after.

Section 1: Warm-up (5 min)

1. “Tell me about your React project.”
2. “Why React over vanilla JS for that project?”
3. “What was hardest to learn in React?”

Section 2: Core Concepts (10 min)

1. “What is JSX?”
2. “Props vs state?”
3. “What is the virtual DOM?”
   • Follow-up: “What triggers a re-render?”
4. “Controlled vs uncontrolled components?”

Section 3: Hooks Deep Dive (10 min)

1. “Explain useState. When use functional updates?”
2. “Explain useEffect — dependency array and cleanup.”
   • Follow-up: “When should you NOT use useEffect?”
3. “useRef vs useState?”
4. “Difference between useMemo and useCallback?”

Section 4: Live Coding (12 min)

Pick ONE:

Option A: Counter with step

“Build a counter. User can set step size. Use useState.”

Option B: Fetch users

“Fetch users from API. Show loading, error, and list. useEffect.”

Option C: Todo with useReducer

“Todo list: add, toggle, delete. Use useReducer.”

Follow-ups:

• “Add delete with event delegation equivalent in React?”
• “Why key={id} not key={index}?”

Section 5: Architecture & Performance (5 min)

1. “Where would you put authentication state?”
2. “How prevent unnecessary re-renders?”
3. “React.memo — when helps, when doesn’t?”

Section 6: Project Connection (3 min)

1. “Walk through your component tree.”
2. “One thing you’d refactor?”
3. “How do you handle API errors?”

Evaluation Rubric

Debrief

Redo weakest hook from hooks-deep-dive.md. Re-attempt Section 4 in 8 minutes.