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import React from "react";
let on = false;
export function getReverseScrollPosition(): number {
if (document.documentElement.scrollHeight <= window.innerHeight) {
return 0;
} else {
return (
document.documentElement.scrollHeight -
document.documentElement.scrollTop -
window.innerHeight
);
}
}
export function scrollToReverseScrollPosition(reversePosition: number): void {
if (document.documentElement.scrollHeight <= window.innerHeight) return;
const old = document.documentElement.style.scrollBehavior;
document.documentElement.style.scrollBehavior = "auto";
window.scrollTo(
0,
document.documentElement.scrollHeight - window.innerHeight - reversePosition
);
document.documentElement.style.scrollBehavior = old;
}
let scrollPosition = getReverseScrollPosition();
const scrollListener = (): void => {
scrollPosition = getReverseScrollPosition();
};
const resizeObserver = new ResizeObserver(() => {
scrollToReverseScrollPosition(scrollPosition);
});
export default function useReverseScrollPositionRemember(): void {
React.useEffect(() => {
if (on) return;
on = true;
window.addEventListener("scroll", scrollListener);
resizeObserver.observe(document.documentElement);
return () => {
window.removeEventListener("scroll", scrollListener);
resizeObserver.disconnect();
on = false;
};
}, []);
}
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