fix: use mouseover+mousemove for preloading to reduce events by dummdidumm · Pull Request #16325 · sveltejs/kit

dummdidumm · 2026-07-10T21:37:11Z

Instead of always firing the mousemove event, we first use mouseover which fires less often, and only if we enter a link we start the mousemove logic. We do that to preserve the "mouse comes to a rest" behavior of the previous solution.

Closes #12664

Instead of always firing the mousemove event, we first use mouseover which fires less often, and only if we enter a link we start the mousemove logic. We do that to preserve the "mouse comes to a rest" behavior of the previous solution. Closes #12664

pkg-svelte-dev · 2026-07-10T21:37:14Z

Install the latest version of @sveltejs/kit from 8fe0bfd:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/8fe0bfd8046d8e7c019bfdbbb6dd7bb09150f64f

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16325

changeset-bot · 2026-07-10T21:37:15Z

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Latest commit: 8fe0bfd

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

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svelte-docs-bot · 2026-07-10T21:38:49Z

Preview: https://svelte-dev-git-preview-kit-16325-svelte.vercel.app/

elliott-with-the-longest-name-on-github · 2026-07-10T22:17:40Z

+		clear_hover_preload();
+		hovered_a = a;
+		start_hover_preload();
+		// Instead of just preloading right away, we start a mousemove listener to implement
+		// "mouse comes to a rest" behavior. This avoid false positives when you just move
+		// your mouse across the screen and happen to pass over a link.
+		container.addEventListener('mousemove', mousemove);


Doesn't mousemove immediately call start_hover_preload again if you move your mouse at all, which clears the timeout and starts it over?

yes, but theoretically there could be no mousemove event after the mouseover, so it's safer to start the hover preload on mouseover, too.

…never removed, cancelling hover-preload for the newly-hovered adjacent anchor This commit fixes the issue reported at packages/kit/src/runtime/client/client.js:2120 ## Bug In `setup_preload()` (`packages/kit/src/runtime/client/client.js`), each preloadable anchor gets two listeners on `mouseover`: ```js a.addEventListener('mousemove', start_hover_preload); a.addEventListener('mouseleave', clear_hover_preload, { once: true }); ``` But `clear_hover_preload()` only removed the `mousemove` listener: ```js function clear_hover_preload() { clearTimeout(mousemove_timeout); hovered_a?.removeEventListener('mousemove', start_hover_preload); hovered_a = undefined; } ``` The `mouseleave` listener on the previous anchor is left attached. ### Trigger: moving the cursor directly from anchor A to adjacent anchor B Per the DOM UI Events spec, moving from element A to a sibling B dispatches events in this order: ``` mouseout(A) → mouseover(B) → mouseleave(A) → mouseenter(B) ``` Note `mouseover(B)` fires **before** `mouseleave(A)`. 1. Hovering A: `hovered_a = A`; A has `mousemove` + `mouseleave` (once) listeners. 2. `mouseover(B)` bubbles to `container`: `find_anchor` returns B, `B !== A`, so `clear_hover_preload()` runs (clears timeout, removes only `mousemove` from A). Then `hovered_a = B`, B gets its listeners, and `start_hover_preload()` schedules B's preload timeout. **A's `mouseleave` listener is still attached.** 3. `mouseleave(A)` now fires the still-attached once-listener → `clear_hover_preload()` runs again → `clearTimeout` cancels B's just-scheduled preload, removes `mousemove` from `hovered_a` (now B), and sets `hovered_a = undefined`. Net result: B never preloads on hover. In a nav menu / list of adjacent links this breaks hover-preload for essentially every direct link-to-link transition. ## Fix Remove the `mouseleave` listener inside `clear_hover_preload` as well: ```js function clear_hover_preload() { clearTimeout(mousemove_timeout); hovered_a?.removeEventListener('mousemove', start_hover_preload); hovered_a?.removeEventListener('mouseleave', clear_hover_preload); hovered_a = undefined; } ``` During step 2, `clear_hover_preload()` now runs while `hovered_a` is still A, so A's `mouseleave` listener is removed *before* the browser dispatches `mouseleave(A)`. The stale handler therefore never fires, and B's preload survives. (Even though the listener was registered with `{ once: true }`, the browser only auto-removes it upon dispatch; explicit removal before dispatch prevents the firing.) Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com> Co-authored-by: Rich-Harris <hello@rich-harris.dev>

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⚠️ # Releases ## @sveltejs/kit@3.0.0-next.8 ### Major Changes - breaking: remove `experimental.handleRenderingErrors` flag ([#16265](#16265)) - breaking: make `getRequest` and `setResponse` synchronous ([#16280](#16280)) - breaking: make `page.url` immutable on a type level ([#16256](#16256)) - breaking: add `refreshAll` and deprecate `invalidateAll` ([#16289](#16289)) ### Minor Changes - feat: allow hyphens in param and matcher names ([#16284](#16284)) - feat: add `ErrorProps` to generated types ([#16272](#16272)) ### Patch Changes - fix: detect destructured `load` and `actions` exports during type generation ([#16329](#16329)) - fix: ensure CSS URL references are absolute when `paths.relative` is `false` ([#16315](#16315)) - fix: exclude deleted cookies from `cookies.getAll()` so it stays consistent with `cookies.get()` ([#16297](#16297)) - fix: reset failed `<svelte:boundary>` on client navigation so a stale `+error.svelte` is torn down ([#16296](#16296)) - fix: preserve shared client chunk hashes when the app version changes ([#16324](#16324)) - fix: align MAX_COOKIE_SIZE with RFC 6265bis ([#16322](#16322)) - fix: use mouseover+mousemove for preloading to reduce events ([#16325](#16325)) ## @sveltejs/package@3.0.0-next.2 ### Minor Changes - feat: warn when using a `.server.` file or file inside a `server` directory without importing a server-only module ([#16266](#16266)) ## @sveltejs/adapter-auto@8.0.0-next.1 ### Patch Changes - fix: allow prerelease versions of SvelteKit 3 to satisfy the peer dependency range ([#16286](#16286)) - Updated dependencies [[`737d119`](737d119), [`fa78efb`](fa78efb), [`07c207e`](07c207e), [`a47071b`](a47071b), [`14d7d5a`](14d7d5a), [`5c38e51`](5c38e51), [`0702baa`](0702baa), [`e1938c6`](e1938c6), [`8293144`](8293144), [`f76d7d9`](f76d7d9), [`ab5c253`](ab5c253), [`b557b1b`](b557b1b), [`4a513e2`](4a513e2)]: - @sveltejs/kit@3.0.0-next.8 ## @sveltejs/adapter-cloudflare@8.0.0-next.2 ### Patch Changes - fix: allow prerelease versions of SvelteKit 3 to satisfy the peer dependency range ([#16286](#16286)) - Updated dependencies [[`737d119`](737d119), [`fa78efb`](fa78efb), [`07c207e`](07c207e), [`a47071b`](a47071b), [`14d7d5a`](14d7d5a), [`5c38e51`](5c38e51), [`0702baa`](0702baa), [`e1938c6`](e1938c6), [`8293144`](8293144), [`f76d7d9`](f76d7d9), [`ab5c253`](ab5c253), [`b557b1b`](b557b1b), [`4a513e2`](4a513e2)]: - @sveltejs/kit@3.0.0-next.8 ## @sveltejs/adapter-netlify@7.0.0-next.3 ### Patch Changes - fix: include `utils.js` in package.json `files` ([#16298](#16298)) - Updated dependencies [[`737d119`](737d119), [`fa78efb`](fa78efb), [`07c207e`](07c207e), [`a47071b`](a47071b), [`14d7d5a`](14d7d5a), [`5c38e51`](5c38e51), [`0702baa`](0702baa), [`e1938c6`](e1938c6), [`8293144`](8293144), [`f76d7d9`](f76d7d9), [`ab5c253`](ab5c253), [`b557b1b`](b557b1b), [`4a513e2`](4a513e2)]: - @sveltejs/kit@3.0.0-next.8 ## @sveltejs/adapter-node@6.0.0-next.3 ### Patch Changes - fix: allow prerelease versions of SvelteKit 3 to satisfy the peer dependency range ([#16286](#16286)) - Updated dependencies [[`737d119`](737d119), [`fa78efb`](fa78efb), [`07c207e`](07c207e), [`a47071b`](a47071b), [`14d7d5a`](14d7d5a), [`5c38e51`](5c38e51), [`0702baa`](0702baa), [`e1938c6`](e1938c6), [`8293144`](8293144), [`f76d7d9`](f76d7d9), [`ab5c253`](ab5c253), [`b557b1b`](b557b1b), [`4a513e2`](4a513e2)]: - @sveltejs/kit@3.0.0-next.8 ## @sveltejs/adapter-static@4.0.0-next.1 ### Patch Changes - fix: allow prerelease versions of SvelteKit 3 to satisfy the peer dependency range ([#16286](#16286)) - Updated dependencies [[`737d119`](737d119), [`fa78efb`](fa78efb), [`07c207e`](07c207e), [`a47071b`](a47071b), [`14d7d5a`](14d7d5a), [`5c38e51`](5c38e51), [`0702baa`](0702baa), [`e1938c6`](e1938c6), [`8293144`](8293144), [`f76d7d9`](f76d7d9), [`ab5c253`](ab5c253), [`b557b1b`](b557b1b), [`4a513e2`](4a513e2)]: - @sveltejs/kit@3.0.0-next.8 ## @sveltejs/adapter-vercel@7.0.0-next.2 ### Patch Changes - fix: allow prerelease versions of SvelteKit 3 to satisfy the peer dependency range ([#16286](#16286)) - Updated dependencies [[`737d119`](737d119), [`fa78efb`](fa78efb), [`07c207e`](07c207e), [`a47071b`](a47071b), [`14d7d5a`](14d7d5a), [`5c38e51`](5c38e51), [`0702baa`](0702baa), [`e1938c6`](e1938c6), [`8293144`](8293144), [`f76d7d9`](f76d7d9), [`ab5c253`](ab5c253), [`b557b1b`](b557b1b), [`4a513e2`](4a513e2)]: - @sveltejs/kit@3.0.0-next.8 Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

elliott-with-the-longest-name-on-github reviewed Jul 10, 2026

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teemingc linked an issue Jul 12, 2026 that may be closed by this pull request

mousemove event listener is being attached in setup_preload even if I am not using data-sveltekit-preload-[x]="hover" #12664

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teemingc reviewed Jul 13, 2026

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Comment thread packages/kit/src/runtime/client/client.js

teemingc reviewed Jul 13, 2026

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Comment thread packages/kit/src/runtime/client/client.js Outdated

Rich-Harris added 3 commits July 13, 2026 16:53

simplify a bit

b1c8ec8

shuffle, so we can early-exit

ac4856e

return early if no preloading will happen

f0e14d2

Rich-Harris approved these changes Jul 13, 2026

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vercel Bot reviewed Jul 13, 2026

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Comment thread packages/kit/src/runtime/client/client.js

Rich-Harris merged commit 4a513e2 into version-3 Jul 14, 2026
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Rich-Harris deleted the mousemover-mouseover branch July 14, 2026 01:56

github-actions Bot mentioned this pull request Jul 14, 2026

Version Packages (next) #16282

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fix: use mouseover+mousemove for preloading to reduce events#16325

fix: use mouseover+mousemove for preloading to reduce events#16325
Rich-Harris merged 5 commits into
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mousemover-mouseover

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