This is the direction of the last scroll action, i.e. compared to the
last scroll event, not necessarily based on the deltas compared to the
last time this callback was called.
scrollHeight: number
scrollLeft: number
scrollLeftFraction: number
This is the scrollLeft relative to the full scrollWidth minus the
clientWidth, ranging from 0 to 1.
scrollTop: number
scrollTopFraction: number
This is the scrollTop relative to the full scrollHeight minus the
clientHeight, ranging from 0 to 1.
This is the direction of the last scroll action, i.e. compared to the last scroll event, not necessarily based on the deltas compared to the last time this callback was called.