Web API, Intersection Observer - Performant Scroll Detection

If you need to observe elements and how they intersect with other elements on the screen - which usually is a scrolling concern; the Intersection Observer is for you! This super simple Web API is built into your browser, widely supported and performant out of the box. In this example I show a simple "image lazy loader" but you can do much much more. Intersection Observer: https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API