Intersection Observer has been implemented in Chrome since 51, and Opera since 38. It's currently being implemented in Firefox ( https://bugzilla.mozilla.org/show_bug.cgi?id=1243846 ), and is "likely" from Edge (https://developer.microsoft.com/en-us/microsoft-edge/platfor... ).
in-view.js's API is certainly less likely to be the cross-platform API than Intersection Observer. Also, plenty of APIs are implemented by browsers at the editor's draft stage.
Intersection Observer has been implemented in Chrome since 51, and Opera since 38. It's currently being implemented in Firefox ( https://bugzilla.mozilla.org/show_bug.cgi?id=1243846 ), and is "likely" from Edge (https://developer.microsoft.com/en-us/microsoft-edge/platfor... ).
in-view.js's API is certainly less likely to be the cross-platform API than Intersection Observer. Also, plenty of APIs are implemented by browsers at the editor's draft stage.