React Internals

Virtual DOM, reconciliation, fiber architecture, concurrent features, and rendering.

Overview

Understanding React internals helps write optimized code and debug complex issues.

Key Concepts

• Virtual DOM — Lightweight representation of the real DOM
• Fiber — Reimplementation enabling concurrent rendering
• Reconciliation — Algorithm comparing virtual DOM trees
• Concurrent Mode — Interruptible rendering for better responsiveness
• Suspense — Defer rendering until data is ready

Code Examples

// Concurrent features
import { startTransition, useDeferredValue } from 'react';

function SearchResults({ query }) {
  const deferredQuery = useDeferredValue(query);
  const isStale = query !== deferredQuery;

  return (
    <div style={{ opacity: isStale ? 0.5 : 1 }}>
      <ResultsList query={deferredQuery} />
    </div>
  );
}

function App() {
  const [query, setQuery] = useState('');

  const handleChange = (e) => {
    startTransition(() => {
      setQuery(e.target.value);
    });
  };

  return (
    <div>
      <input value={query} onChange={handleChange} />
      <SearchResults query={query} />
    </div>
  );
}

Practice

Build a search app that uses concurrent features to keep the UI responsive during large list renders.