fix: update sveltekit:prefetch mouse detection (#2995)

* dispatch custom event - fixes #2929

* changeset

* missing semicolon

* clarify pull request

* pnpm check

* update typescript check

* Update packages/kit/src/runtime/client/router.js

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

.changeset/lazy-ways-swim.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix `sveltekit:prefetch` mouse detection

packages/kit/src/runtime/client/router.js

@@ -94,7 +94,7 @@ export class Router {
 			}, 200);
 		});
 
-		/** @param {MouseEvent|TouchEvent} event */
+		/** @param {Event} event */
 		const trigger_prefetch = (event) => {
 			const a = find_anchor(event);
 			if (a && a.href && a.hasAttribute('sveltekit:prefetch')) {
@@ -109,12 +109,17 @@ export class Router {
 		const handle_mousemove = (event) => {
 			clearTimeout(mousemove_timeout);
 			mousemove_timeout = setTimeout(() => {
-				trigger_prefetch(event);
+				// event.composedPath(), which is used in find_anchor, will be empty if the event is read in a timeout
+				// add a layer of indirection to address that
+				event.target?.dispatchEvent(
+					new CustomEvent('sveltekit:trigger_prefetch', { bubbles: true })
+				);
 			}, 20);
 		};
 
 		addEventListener('touchstart', trigger_prefetch);
 		addEventListener('mousemove', handle_mousemove);
+		addEventListener('sveltekit:trigger_prefetch', trigger_prefetch);
 
 		/** @param {MouseEvent} event */
 		addEventListener('click', (event) => {