Press n or j to go to the next uncovered block, b, p or k for the previous block.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 | 1x 1x 8x 8x 8x 8x 8x 8x 8x 3x 3x 5x 5x 5x 1x 3x 3x 3x 3x 3x 3x | /**
* Pure scroll-math utilities for the smart-scroll feature.
* No DOM or React dependencies — easy to unit test.
*/
/** Pixel threshold for "near anchor" detection. */
export const SCROLL_ANCHOR_THRESHOLD_PX: number = 50;
/**
* Whether the scroll position is within threshold of the anchor point.
*
* @param scrollTop - Current scrollTop of the container
* @param scrollHeight - Total scrollable height of the container
* @param clientHeight - Visible height of the container
* @param isReversed - If true, anchor is at the top; otherwise at bottom
* @param threshold - Override the default 50px threshold
* @returns True if the scroll position is near the anchor
*/
export function isNearAnchor(
scrollTop: number,
scrollHeight: number,
clientHeight: number,
isReversed: boolean,
threshold: number = SCROLL_ANCHOR_THRESHOLD_PX,
): boolean {
if (isReversed) {
// Anchor is at the top — near anchor when scrollTop is small
return scrollTop < threshold;
}
// Anchor is at the bottom — near anchor when close to max scroll
const distanceFromBottom = scrollHeight - scrollTop - clientHeight;
return distanceFromBottom < threshold;
}
/**
* Compute the scrollTop delta needed to compensate for prepended content.
* Used in reverse mode to prevent viewport shift when new items appear at top.
*
* @param previousScrollHeight - scrollHeight before the render
* @param currentScrollHeight - scrollHeight after the render
* @returns Positive delta to add to scrollTop, or 0 if no compensation needed
*/
export function computeScrollCompensation(
previousScrollHeight: number,
currentScrollHeight: number,
): number {
const delta = currentScrollHeight - previousScrollHeight;
return delta > 0 ? delta : 0;
}
|