Implementation status:
- Chromium: Shipped in Chrome 51
- Edge: Shipped in build 14986
- Firefox: Shipped in Firefox 55
- WebKit: Shipped in Safari 12.1 and iOS 12.2
Given that multiple native implementations of IntersectionObserver exist today, the polyfill that was formerly maintained in this repo is no longer supported and has been archived at https://github.com/GoogleChromeLabs/intersection-observer.