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Fix cross-route fragment scrolling #163

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Fix cross-route fragment scrolling #163

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5 changes: 5 additions & 0 deletions .changeset/calm-anchors-scroll.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'preact-iso': patch
---

Scroll cross-route URL fragments to matching IDs or named anchors after the destination route commits.
22 changes: 21 additions & 1 deletion src/router.js
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,26 @@ function isInScope(href) {
);
}

/** @param {string} url */
function scrollToUrl(url) {
const hash = new URL(url, location.origin).hash;
if (hash) {
try {
const fragment = decodeURIComponent(hash.slice(1));
const target = document.getElementById(fragment) ||
Array.from(document.getElementsByName(fragment)).find(
element => element.localName == 'a'
);
Comment on lines +33 to +35

@rschristian rschristian Aug 23, 2026 •
edited
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I don't know that we really need to support this, as it's super niche, but this can be done simpler:

Suggested change
Array.from(document.getElementsByName(fragment)).find(
element => element.localName == 'a'
);
document.querySelector(`a[name="${fragment}"`);

@JoviDeCroock JoviDeCroock Aug 24, 2026

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I wanted to avoid potential CSS injection issues mainly

if (target) {
target.scrollIntoView();
return;
}
} catch {}
}

scrollTo(0, 0);
}

/**
* @param {string} state
* @param {MouseEvent | PopStateEvent | { url: string, replace?: boolean }} action
Expand Down Expand Up @@ -274,7 +294,7 @@ export function Router(props) {

// The route is loaded and rendered.
if (prevRoute.current !== path) {
if (wasPush) scrollTo(0, 0);
if (wasPush) scrollToUrl(url);
if (props.onRouteChange) props.onRouteChange(url);

prevRoute.current = path;
Expand Down
7 changes: 6 additions & 1 deletion test/router.test.js
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Expand Up @@ -775,13 +775,15 @@ describe('Router', () => {
scrollTo.restore();
});

it('should ignore clicks on document fragment links', async () => {
it('should handle document fragment links', async () => {
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const pushState = sinon.spy(history, 'pushState');
const scrollIntoView = sinon.spy(Element.prototype, 'scrollIntoView');

const Route = sinon.fake(
() => <div>
<a href="#foo">just #foo</a>
<a href="/other#bar">other #bar</a>
<a name="bar">bar target</a>
</div>
);
render(
Expand Down Expand Up @@ -815,8 +817,11 @@ describe('Router', () => {
expect(loc).to.deep.include({ url: '/other#bar', path: '/other' });
expect(pushState).to.have.been.called;
expect(location.hash).to.equal('#bar');
expect(scrollIntoView).to.have.been.calledOnce;
expect(scrollIntoView).to.have.been.calledOn(scratch.querySelector('a[name="bar"]'));

pushState.restore();
scrollIntoView.restore();
});

it('should ignore clicks on download links', async () => {
Expand Down