IntersectionObserver for Scroll-Triggered Effects
Use IntersectionObserver inside useEffect to trigger animations, lazy loading, and infinite scroll.
What IntersectionObserver Does
The IntersectionObserver API efficiently monitors whether one or more elements enter or leave the browser viewport (or a specified ancestor element). Unlike scroll listeners that fire on every pixel, the observer only calls your callback when the element crosses a threshold, making it far more performant for scroll-based effects.
The Observer Callback and Entry
The callback receives an array of IntersectionObserverEntry objects, one per observed element. Each entry has an isIntersecting boolean (true when visible) and an intersectionRatio number between 0 and 1 (fraction of the element currently visible). Use these to determine visibility state.
All lessons in this course
- Clipboard API: Copy and Paste in React
- Geolocation API in React Components
- Notifications API and Permission Handling
- IntersectionObserver for Scroll-Triggered Effects