Q29: How do you implement Optimistic UI updates with the useOptimistic Hook in React 19?

React 19's useOptimistic hook allows immediately displaying an optimistic state result to users while a server background mutation is pending. If the network request fails, React rolls back the state automatically.

React 19 useOptimistic Hook Usage

import { useOptimistic } from 'react';

function Thread({ messages, sendMessage }) {
  const [optimisticMessages, addOptimisticMessage] = useOptimistic(
    messages,
    (state, newText) => [...state, { text: newText, sending: true }]
  );

  const formAction = async (formData) => {
    const text = formData.get('message');
    addOptimisticMessage(text); // Immediately update UI
    await sendMessage(text);     // Perform actual network mutation
  };
}

💡 useOptimistic immediately appends the pending message to state while sendMessage executes.

Key Takeaways

Improves perceived latency by rendering expected mutation responses immediately.
Rolls back state safely if the background network action fails.

Knowledge Check

What primary user experience benefit does Optimistic UI provide?

Q29: How do you implement Optimistic UI updates with the useOptimistic Hook in React 19?

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