What's New in React 19.1

React 19.1 has just been released, bringing several exciting features and improvements. Let's dive into what's new.

useOptimistic Hook

The new useOptimistic hook allows you to show optimistic updates while an async operation is in progress:

const [optimisticState, addOptimistic] = useOptimistic(
  state,
  (currentState, optimisticValue) => {
    return [...currentState, optimisticValue];
  }
);

This is particularly useful for forms and real-time updates where you want to show immediate feedback.

Server Components Improvements

Server Components now support better streaming with improved chunk management. This means faster initial page loads and better progressive rendering.

Key improvements include:

• Enhanced streaming SSR performance
• Better error handling in Server Actions
• Improved ReactDOM.preload support for preloading resources

Better Error Messages

Hydration mismatch errors now provide more detailed information about what went wrong, making debugging much easier. The new error messages include:

• Exact location of the mismatch
• Expected vs actual content comparison
• Suggestions for common fixes

Conclusion

React 19.1 is a solid release that continues to improve the developer experience. The useOptimistic hook alone makes the upgrade worthwhile.