IntersectionObserver

While passive event listeners are an improvement, they are not a complete solution. It's more like the "least of evils". There is a new set of primitives that is being implemented called IntersectionObserver which solves most of the issues of having to detect when something is in view + they run on a separate thread. So you don't need to do any computations, reading the window size and whatnot magic to detect if an element is inside the window. We are currently using this in prod for our algolia static websites and it has worked very well for the majority of all of our use cases. https://github.com/WICG/IntersectionObserver/blob/gh-pages/e...

Use the polyfill from WICG - https://github.com/WICG/IntersectionObserver/tree/gh-pages/p...

The repository you linked to, actually contains the official polyfill: https://github.com/WICG/IntersectionObserver/tree/gh-pages/p... (it should be about 6 KB minzipped)

There is an emerging standard called Intersection Observer that addresses the same use case: https://github.com/WICG/IntersectionObserver/blob/gh-pages/e... This is a really useful problem to solve. But, I would personally prefer to solve it with a polyfill for a standardized approach that will eventually receive native implementation.