fix: throw an error when prerendering a root +server.js that returns a non-HTML response by geodask · Pull Request #15994 · sveltejs/kit

geodask · 2026-06-09T07:05:20Z

When a root +server.js returns a non-HTML response and is marked as prerenderable, SvelteKit was silently saving the response as index.html. This was caused by output_filename() falling back to 'index.html' when the path slice for the root was an empty string.

The fix throws a clear error at build time instead. There's no valid static filename for a non-HTML response at the root path. A static host will always serve an HTML file for /.

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…a non-HTML response Closes sveltejs#11087

changeset-bot · 2026-06-09T07:05:27Z

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elliott-with-the-longest-name-on-github · 2026-06-12T20:05:27Z

There's no valid static filename for a non-HTML response at the root path. A static host will always serve an HTML file for /.

I don't think this is a true premise. Surely it's possible on most static hosts to configure the root file + mime type, right?

geodask · 2026-06-14T10:53:13Z

This approach was suggested by @Rich-Harris in #14135 (comment). Happy to improve the error message wording if needed

Rich-Harris · 2026-06-16T13:32:45Z

test failures are caused by some inscrutable lockfile nonsense

mostly just trying to unstick whatever's causing CI to fail on #15994

Rich-Harris

thank you!

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [@sveltejs/kit](https://svelte.dev) ([source](https://github.com/sveltejs/kit/tree/HEAD/packages/kit)) | [`2.65.1` → `2.66.0`](https://renovatebot.com/diffs/npm/@sveltejs%2fkit/2.65.1/2.66.0) | ![age](https://developer.mend.io/api/mc/badges/age/npm/@sveltejs%2fkit/2.66.0?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/@sveltejs%2fkit/2.65.1/2.66.0?slim=true) | --- ### Release Notes <details> <summary>sveltejs/kit (@sveltejs/kit)</summary> ### [`v2.66.0`](https://github.com/sveltejs/kit/blob/HEAD/packages/kit/CHANGELOG.md#2660) [Compare Source](https://github.com/sveltejs/kit/compare/@sveltejs/kit@2.65.2...@sveltejs/kit@2.66.0) ##### Minor Changes - feat: precompress prerendered `.md` and `.mdx` files ([#15893](sveltejs/kit#15893)) - feat: warn the user when they forget to make boolean inputs optional in their form schemas ([#15804](sveltejs/kit#15804)) ##### Patch Changes - fix: blur active element before component update during navigation so that blur/focusout handlers fire while old component data is still valid ([#15452](sveltejs/kit#15452)) - fix: ensure `base` is available from `$service-worker` during development ([#15882](sveltejs/kit#15882)) - fix: use correct relative asset paths when rendering an error page for a missing `__data.json` request ([#15884](sveltejs/kit#15884)) - fix: preserve active `for await` consumers across `query.live` reconnects ([#16022](sveltejs/kit#16022)) - fix: settle `query.live` reconnect promise on all exit paths, preventing `invalidateAll()` from deadlocking when a live query is offline or interrupted ([#16022](sveltejs/kit#16022)) - fix: preserve last value when a `query.live` stream completes without yielding on reconnect ([#16022](sveltejs/kit#16022)) - fix: remove `types: ['node']` from generated tsconfig to avoid errors when `@types/node` is not installed ([#15709](sveltejs/kit#15709)) - fix: prefer pages over endpoints when prerendering ([#16076](sveltejs/kit#16076)) - fix: restore snapshots after afterNavigate callbacks ([#16066](sveltejs/kit#16066)) - fix: support `ws:`/`wss:` and `trusted-types-eval` for CSP sources ([#15938](sveltejs/kit#15938)) - fix: omit empty `file` inputs from remote form data ([#15898](sveltejs/kit#15898)) - fix: fail early if a route with `+page` and `+server` is marked as prerenderable ([#16075](sveltejs/kit#16075)) - fix: wait a tick before resetting forms ([#15805](sveltejs/kit#15805)) - fix: `preflight` schemas apply correctly when chained before `for` ([#15863](sveltejs/kit#15863)) - fix: blank page in SPA mode when root layout `load()` throws ([#15798](sveltejs/kit#15798)) - fix: pass all unknown options from the `sveltekit` Vite plugin through to `vite-plugin-svelte` ([#16010](sveltejs/kit#16010)) ### [`v2.65.2`](https://github.com/sveltejs/kit/blob/HEAD/packages/kit/CHANGELOG.md#2652) [Compare Source](https://github.com/sveltejs/kit/compare/@sveltejs/kit@2.65.1...@sveltejs/kit@2.65.2) ##### Patch Changes - fix: throw an error when prerendering a root +server.js that returns a non-HTML response ([#15994](sveltejs/kit#15994)) - fix: decode base64-serialized fetch bodies before caching them for client-side replay ([#16034](sveltejs/kit#16034)) - fix: correctly access explicit dynamic public environment variables from prerendered pages and service workers ([#16024](sveltejs/kit#16024)) - fix: allow `preloadCode` to be called during initial page load ([#16028](sveltejs/kit#16028)) - fix: send `cache-control: private, no-store` on remote function responses so personalized query results can never be cached by shared caches ([#16020](sveltejs/kit#16020)) - fix: preserve the HTTP status and error body when a remote function request fails in transport (e.g. a 401/403 from a `handle` hook), instead of reporting a generic 500 ([#16021](sveltejs/kit#16021)) - fix: avoid loading universal nodes during build analysis when the app uses a hash router ([#16042](sveltejs/kit#16042)) - fix: correctly serve client entry during development when using the pnpm global virtual store ([#16045](sveltejs/kit#16045)) - fix: normalize path separators when comparing config ([#16037](sveltejs/kit#16037)) - fix: ensure `building` resolves correctly to allow avoiding build-time explicit environment variable validation ([#16058](sveltejs/kit#16058)) - fix: prevent unhandled promise rejections when remote function failures are consumed via `current`/`error` instead of `await` ([#16018](sveltejs/kit#16018)) </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Disabled because a matching PR was automerged previously. ♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Mend Renovate](https://github.com/renovatebot/renovate).  Reviewed-on: https://codeberg.org/huskas-2189/Bookmark/pulls/126

…arset parameter (#16567) The prerenderer compares `content-type` with `===`, so `text/html; charset=utf-8` is not treated as HTML: the page is written without a `.html` extension and its links are never crawled. `is_content_type` already normalizes the header for this reason, from #7195 (strip parameters) and GHSA-gv7g-x59x-wf8f (case-insensitive compare); the two prerender checks predate both. Reproduces #13612, closed as unreproducible, using the charset workaround from #3184. The root `+server.js` error added in #15994 is gated on the same value, so it can fire for an app that has none. Co-authored-by: Nic Polumeyv <nicolas.polum@gmail.com> Co-authored-by: Rich Harris <richard.a.harris@gmail.com>

fix: throw an error when prerendering a root +server.js that returns …

a2d0d91

…a non-HTML response Closes sveltejs#11087

Merge branch 'main' into fix/prerender-root-server-js-error

db80048

Rich-Harris and others added 2 commits June 16, 2026 09:17

fix

e0d7e31

Merge branch 'main' into fix/prerender-root-server-js-error

c291ac2

Rich-Harris mentioned this pull request Jun 16, 2026

chore: bump prettier-plugin-svelte #16055

Merged

teemingc added 2 commits June 17, 2026 00:00

Merge branch 'main' into fix/prerender-root-server-js-error

c4998bb

fix lock file

ea4f823

Rich-Harris added a commit that referenced this pull request Jun 16, 2026

chore: bump prettier-plugin-svelte (#16055)

c62ddd0

mostly just trying to unstick whatever's causing CI to fail on #15994

Rich-Harris approved these changes Jun 16, 2026

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Rich-Harris merged commit 80cc084 into sveltejs:main Jun 16, 2026
42 of 44 checks passed

github-actions Bot mentioned this pull request Jun 16, 2026

Version Packages #16050

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Nic-Polumeyv mentioned this pull request Jul 29, 2026

fix: prerender and crawl pages whose content-type header carries a charset parameter #16567

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fix: throw an error when prerendering a root +server.js that returns a non-HTML response - #15994

fix: throw an error when prerendering a root +server.js that returns a non-HTML response#15994
Rich-Harris merged 6 commits into
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geodask:fix/prerender-root-server-js-error

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geodask commented Jun 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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