Function syncNestedStreamScroll

src/hold-stream.ts:184–207

(
  root: HTMLElement,
  options?: { pin?: boolean; smooth?: boolean; factor?: number },
)

 * With `pin: false`, only scroll when the reader is already near the bottom.
 */
export function syncNestedStreamScroll(
  root: HTMLElement,
  options?: { pin?: boolean; smooth?: boolean; factor?: number },
): void {
  const thresholdPx = options?.pin === false ? 80 : Number.POSITIVE_INFINITY;
  const smooth = options?.smooth ?? false;
  const factor = options?.factor ?? DEFAULT_STREAM_SCROLL_EASE;

  root.querySelectorAll(NESTED_SCROLL_SELECTOR).forEach((node) => {
    const el = node as HTMLElement;
    if (!isVerticallyScrollable(el)) {
      return;
    }
    const distanceFromBottom =
      el.scrollHeight - el.scrollTop - el.clientHeight;
    if (distanceFromBottom <= thresholdPx) {
      if (smooth) {
        easeScrollToBottom(el, factor);
      } else {
        el.scrollTop = el.scrollHeight;
      }
    }
  });
}