The most basic usage of ScrollTrigger is to trigger classes based on the current scroll position. E.g. when an element enters the viewport, fade it in. You can add custom offsets per element, or set offsets on the viewport (e.g. always trigger after the element reaches 20% of the viewport) When using the callbacks ScrollTrigger becomes really powerful. You can run custom code when an element enters/becomes visible, and even return Promises to halt the trigger if the callback fails. ...