How do useTransition, Suspense, and useDeferredValue work together in React 18+ to improve UI responsiveness during expensive state updates?

A common pattern in React apps: typing into a search input that triggers expensive rendering (e.g., filtering a long list or drawing thousands of items). This explores how React’s concurrent APIs help keep the UI responsive.

React 18’s useTransition hook lets you mark non urgent UI updates—like re-rendering a long list—as low-priority transitions. When wrapped inside startTransition, React delays those updates if something urgent happens (like typing in an input), keeping the UI snappy. Simultaneously, isPending helps show a “spinning” fallback or disable buttons during the transition.  Meanwhile, using <Suspense> boundaries (typically around lazily loaded UI or async data) lets React delay showing incomplete content and reveal fallback UIs while it's loading. When transitioning route changes or component loads, Suspense can help smoothly reveal subtrees without freezing the main thread. useDeferredValue is useful when you want part of your app to “lag behind” synchronously-updated props or context—like deferring a search filter to the slow list rendering. You derive a deferred version of your fast-updating state which updates in the background, keeping inputs responsive. Key interactions: • State updates inside startTransition become interruptible. High-priority updates (like input) interrupt transitions, React waits, then resumes rendering the transition. • Suspense boundaries suspend rendering until loaded, without blocking the rest of the UI. • useDeferredValue avoids typing lag by delaying expensive re-rendering without startTransition. Tags: React 18, useTransition, Suspense, useDeferredValue, concurrent rendering