(sorry, bad title)
This was originally filed against the IntersectionObserver spec: https://github.com/w3c/IntersectionObserver/issues/472
1. go to https://jsfiddle.net/90sw7dhf/
2. scroll down
Expected: in Firefox and Chrome, alternating green and blue divs, infinitely
Actual: in Safari TP, green turns blue, then a different shade of blue and that's it.
The jsfiddle has a log, and it seems like it's looping forever when trying to log "wow".
Created attachment 460325 [details]
In both Chrome and Firefox there's a scroll position jump that happens when the elements are moved around. That might be a side effect of scroll anchoring, which Safari doesn't have.
Something similar happens in Firefox if I disable scroll anchoring, and that makes sense; moving the elements changes their intersection, which fires the callbacks, which changes the content.