Skip to content

fix(site): scroll-spy highlights the last guide section at page bottom #207

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
Exoridus merged 1 commit into from
Jun 27, 2026
Merged

fix(site): scroll-spy highlights the last guide section at page bottom #207

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
51 changes: 33 additions & 18 deletions site/src/pages/en/guide/[part]/[chapter]/index.astro
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -194,28 +194,43 @@ const sidebarParts = GUIDE_PARTS.map(part => ({
}
if (map.size === 0) return;

const headings = [...map.keys()];
if (headings.length === 0) return;

const setActive = (link) => {
links.forEach(node => node.setAttribute('data-active', 'false'));
link.setAttribute('data-active', 'true');
links.forEach(node => node.setAttribute('data-active', String(node === link)));
};

const observer = new IntersectionObserver(
entries => {
const visible = entries
.filter(entry => entry.isIntersecting)
.sort((a, b) => a.boundingClientRect.top - b.boundingClientRect.top);
const top = visible[0];
if (!top) return;
const link = map.get(top.target);
if (link) setActive(link);
},
{ rootMargin: '-20% 0px -65% 0px', threshold: [0, 1] },
);

for (const heading of map.keys()) observer.observe(heading);
// Active = the last heading whose top has crossed a line ~28% down the
// viewport. A rootMargin "band" can't do this: headings near the page
// bottom never scroll high enough to enter the band, so the final
// section(s) would never activate. At the very bottom we force the last
// heading, since it can sit below the line with nothing left to scroll.
const LINE = 0.28;
const update = () => {
const line = window.innerHeight * LINE;
let active = headings[0];
for (const heading of headings) {
if (heading.getBoundingClientRect().top <= line) active = heading;
else break;
}
const atBottom = window.innerHeight + window.scrollY >= document.documentElement.scrollHeight - 4;
if (atBottom) active = headings[headings.length - 1];
setActive(map.get(active));
};

const firstLink = links[0];
if (firstLink instanceof HTMLAnchorElement) setActive(firstLink);
let ticking = false;
const onScroll = () => {
if (ticking) return;
ticking = true;
requestAnimationFrame(() => {
ticking = false;
update();
});
};
window.addEventListener('scroll', onScroll, { passive: true });
window.addEventListener('resize', onScroll, { passive: true });
update();
})();
</script>

Expand Down