[fix] transform links to be absolute to avoid console error when navigating

.changeset/stupid-dolls-fly.md

@@ -0,0 +1,5 @@
+---
+"@sveltejs/kit": patch
+---
+
+[fix] transform link[rel=icon] to be absolute to avoid console error when navigating

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

@@ -1220,6 +1220,13 @@ export function create_client({ target, session, base, trailing_slash }) {
 				}
 			});
 
+			// fix link[rel=icon], because browsers will occasionally try to load relative
+			// URLs after a pushState/replaceState, resulting in a 404 — see
+			// https://github.com/sveltejs/kit/issues/3748#issuecomment-1125980897
+			for (const link of document.querySelectorAll('link')) {
+				if (link.rel === 'icon') link.href = link.href;
+			}
+
 			addEventListener('pageshow', (event) => {
 				// If the user navigates to another site and then uses the back button and
 				// bfcache hits, we need to set navigating to null, the site doesn't know

packages/kit/test/apps/basics/test/test.js

@@ -1043,15 +1043,29 @@ test.describe('$app/paths', () => {
 		);
 	});
 
-	test('replaces %sveltekit.assets% in template with relative path', async ({ page }) => {
+	// some browsers will re-request assets after a `pushState`
+	// https://github.com/sveltejs/kit/issues/3748#issuecomment-1125980897
+	test('replaces %sveltekit.assets% in template with relative path, and makes it absolute in the client', async ({
+		baseURL,
+		page,
+		javaScriptEnabled
+	}) => {
+		const absolute = `${baseURL}/favicon.png`;
+
 		await page.goto('/');
-		expect(await page.getAttribute('link[rel=icon]', 'href')).toBe('./favicon.png');
+		expect(await page.getAttribute('link[rel=icon]', 'href')).toBe(
+			javaScriptEnabled ? absolute : './favicon.png'
+		);
 
 		await page.goto('/routing');
-		expect(await page.getAttribute('link[rel=icon]', 'href')).toBe('./favicon.png');
+		expect(await page.getAttribute('link[rel=icon]', 'href')).toBe(
+			javaScriptEnabled ? absolute : './favicon.png'
+		);
 
 		await page.goto('/routing/rest/foo/bar/baz');
-		expect(await page.getAttribute('link[rel=icon]', 'href')).toBe('../../../../favicon.png');
+		expect(await page.getAttribute('link[rel=icon]', 'href')).toBe(
+			javaScriptEnabled ? absolute : '../../../../favicon.png'
+		);
 	});
 });