fix: abort superseded preloads - #17080
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When a `data-sveltekit-preload-data` preload is superseded by a preload for another link, its in-flight requests are now aborted instead of running to completion. The `AbortSignal` is threaded through `load_route` into both the `__data.json` request and the `fetch` passed to `load`. Aborting only happens while the preload is still speculative — once its token has been consumed by a real navigation, `discard_load_cache` leaves it alone so the navigation the user asked for isn't cancelled. `preloadData()` is unaffected: it passes no `AbortController`, so its requests are never cancelled by a subsequent preload. Two related fixes: - a superseded preload rejects after `load_cache` has already been replaced, so the rejection handler now only discards the cache when it still owns it - `discard_load_cache` attached no rejection handler to `load_cache.fork`, which turned every aborted preload into an unhandled rejection under `experimental.forkPreloads`
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Install the latest version of pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/56bf4fefff27fb63918a0251d753dedc3454f51eOpen in Note This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed. |
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gcamargosilva
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September 9, 2026 16:47
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| }); | ||
| } else { | ||
| void _preload_data(intent); | ||
| void _preload_data(intent, true); |
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| void _preload_data(intent, true); | |
| // swallow rejections (e.g. AbortError when this preload is superseded and | |
| // its controller is aborted) so they do not surface as unhandled rejections | |
| void _preload_data(intent, true).catch(() => {}); |
In production builds, superseding an in-flight cancellable preload triggers an unhandled promise rejection (AbortError) because the non-DEV void _preload_data(intent, true) call has no .catch.
gcamargosilva
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September 9, 2026 16:58
gcamargosilva
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September 9, 2026 17:39
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Hello guys,
I'm not sure if this is a specific edge case, but I have an Svelte app with many links where some preloads can take 1s+.
When hovering over multiple links, the previous preloads keep running even after they've been superseded. When the user clicks a link, this can make the navigation wait for those previous preloads to finish.
During the investigation, I noticed that preloads don't have an
AbortController, so I couldn't find a way to cancel these requests.Proposed fix
This PR aborts in-flight requests when a speculative preload is superseded by a newer one.
The signal is propagated through
load_routeto both the__data.jsonrequest and thefetchavailable toloadfunctions.Once a preload is consumed by a real navigation, it is no longer aborted, so user-initiated navigation remains unaffected.
I also fixed two related issues around rejected preload promises/unhandled rejections that became apparent while implementing this.
I'm not sure whether this is a broader problem or just an edge case from my application, so feel free to reject this PR if the behavior doesn't make sense for SvelteKit's preload model.
Please don't delete this checklist! Before submitting the PR, please make sure you do the following:
Tests
pnpm testand lint the project withpnpm lintandpnpm checkdata-sveltekit-preload-data aborts a superseded preloadwas verified to fail onversion-3and pass with this change. The fulltest-basicsPlaywright suite passes (693 passed, 0 failed), as dooxfmt --check,eslint, andtsconpackages/kit(the pre-existingsrc/exports/vite/index.jsTS2321 is unrelated and also present onversion-3).Changesets
pnpm changesetand following the prompts. Changesets that add features should beminorand those that fix bugs should bepatch. Please prefix changeset messages withfeat:,fix:, orchore:.Edits