Interruptible Rendering with useTransition

The useTransition hook creates interruptible rendering lanes, allowing expensive state updates to be deprioritized without blocking critical user interactions. When filtering large datasets or processing heavy computations, wrapping the state setter in startTransition means typing in an input remains responsive while the expensive render happens in the background. This eliminates manual debouncing patterns.

React interrupts and resumes work based on priority. High-priority updates like input changes get immediate rendering attention, while transition-marked updates yield to more urgent work.

Architectural Decision Matrix

// Use useTransition when you control the state setter
const [isPending, startTransition] = useTransition();
const [filteredData, setFilteredData] = useState(data);

const handleFilter = (query: string) => {
  startTransition(() => {
    setFilteredData(expensiveFilter(data, query));
  });
};

// Use useDeferredValue when receiving external props
const SearchResults = ({ searchQuery }: Props) => {
  const deferredQuery = useDeferredValue(searchQuery);
  const results = useMemo(() => 
    expensiveFilter(data, deferredQuery), 
    [deferredQuery]
  );
  
  return (
    <div style={{ opacity: searchQuery !== deferredQuery ? 0.5 : 1 }}>
      {results.map(item => <ResultCard key={item.id} {...item} />)}
    </div>
  );
};

The distinction between these primitives maps directly to component ownership boundaries. If your component owns the state update logic, useTransition provides explicit control over which updates should be interruptible. When dealing with props passed from parent components, useDeferredValue creates a lagged version of that value, allowing your component to render with stale data while the fresh expensive render happens in the background.

Progressive Hydration Control with Suspense

Strategic Suspense boundary placement directly impacts SSR hydration performance. React hydrates components progressively, prioritizing interactive elements based on Suspense boundaries. Wrapping non-critical content like comment sections or recommendation widgets in Suspense allows essential features to become interactive first. This means a checkout button can respond to clicks while product reviews are still hydrating.

The granularity of your Suspense boundaries determines hydration chunking. Too few boundaries force React to hydrate large component trees atomically. Too many create excessive overhead from boundary management. The optimal approach identifies natural split points where interactivity matters most, such as separating primary actions from secondary content or isolating heavy client-side features.

Applied Insight

Choose useTransition for state updates you control and need to deprioritize, useDeferredValue for expensive computations driven by external props. Place Suspense boundaries around non-critical interactive features to unlock progressive hydration benefits in SSR applications. Avoid wrapping every state update in transitions or creating Suspense boundaries for static content, as this adds unnecessary complexity without performance gains. These concurrent primitives excel when dealing with genuinely expensive operations that would otherwise degrade user experience.