React 19: Mastering Concurrent Features

React 19 introduces powerful concurrent rendering features that transform how we build performant applications.

Understanding Concurrent Rendering

Concurrent rendering allows React to interrupt rendering work to handle high-priority updates. This means your app stays responsive even during expensive operations.

Key Concepts

• 1. Transitions: Mark updates as non-urgentTransitions: Mark updates as non-urgent
• 2. Suspense: Handle async operations declarativelySuspense: Handle async operations declaratively
• 3. Streaming SSR: Send HTML to the client progressivelyStreaming SSR: Send HTML to the client progressively

Using Transitions

import { useTransition } from 'react';
function SearchResults() {
  const [isPending, startTransition] = useTransition();
  const [query, setQuery] = useState('');
  const handleChange = (e) => {
    startTransition(() => {
      setQuery(e.target.value);
    });
  };
  return (
    

      
      {isPending ?  : }
    
  );
}

Suspense for Data Fetching

React 19 makes Suspense work seamlessly with data fetching:

function ProfilePage() {
  return (
    }>
      
      
    
  );
}

Performance Best Practices

• •Use transitions for filtering, sorting, and navigation
• •Combine Suspense with streaming SSR for faster perceived load times
• •Profile your app with React DevTools Profiler

Conclusion

React 19's concurrent features enable building highly responsive applications that feel instant to users.