perf: use a Set to check element ids when validating fragment links

[Nic-Polumeyv]

Prerendering validates each expected fragment link with hashlinks.includes(id) against the target page's array of element ids, which is O(A*L) for A ids and L inbound fragment links. Storing the crawled ids as a Set makes it O(A + L).

Cost for a page with N anchors and N inbound fragment links (Node 22):

N	array includes	Set (incl. construction)
1,000	21 ms	0.5 ms
4,000	123 ms	0.8 ms
8,000	616 ms	1.7 ms
16,000	1,591 ms	3.8 ms

This mainly benefits large heavily cross-linked prerendered sites such as generated API references.

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from c6ad266:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/c6ad266ec85bdecc00cc54db95c658bdf8458c17

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16494

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: c6ad266

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[teemingc]

Thanks