React useIntersectionObserver Hook Simplifies Lazy Loading and Visibility Tracking

The browser's IntersectionObserver API offers an asynchronous, off-main-thread way to detect when elements enter the viewport, replacing older scroll-listener approaches that caused performance issues. Traditional scroll-based visibility checks using getBoundingClientRect fire dozens of times per second on the main thread, leading to janky scrolling and edge-case failures. Hand-rolled React implementations of IntersectionObserver often ship with three recurring bugs: memory leaks from missing cleanup, stale closures when callbacks reference props or state, and duplicated boilerplate across components. The useIntersectionObserver hook from @reactuses/core centralises this logic, accepting a target ref, a callback, and optional configuration such as threshold, rootMargin, and root. The hook is SSR-safe, fully typed, and covers common use cases including lazy image loading, analytics visibility events, and infinite-scroll sentinels.