From b98aa14184d6c7d15293413ba5a7824c839ae5e7 Mon Sep 17 00:00:00 2001
From: XploitMonk0x01 <ethicalrobo06@gmail.com>
Date: Mon, 16 Mar 2026 01:12:57 +0530
Subject: [PATCH] fix(html): handle trailing slash in transformIndexHtml
 pre-transform

---
 .../middlewares/__tests__/indexHtml.spec.ts   | 29 +++++++++++++++++++
 .../src/node/server/middlewares/indexHtml.ts  |  6 +++-
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 packages/vite/src/node/server/middlewares/__tests__/indexHtml.spec.ts

diff --git a/packages/vite/src/node/server/middlewares/__tests__/indexHtml.spec.ts b/packages/vite/src/node/server/middlewares/__tests__/indexHtml.spec.ts
new file mode 100644
index 00000000000000..11ab318117a858
--- /dev/null
+++ b/packages/vite/src/node/server/middlewares/__tests__/indexHtml.spec.ts
@@ -0,0 +1,29 @@
+import path from 'node:path'
+import { describe, expect, test } from 'vitest'
+import { getHtmlDirnameForRelativeUrl } from '../indexHtml'
+
+describe('getHtmlDirnameForRelativeUrl', () => {
+  test('keeps trailing slash paths unchanged', () => {
+    expect(getHtmlDirnameForRelativeUrl('/example/dir/')).toBe('/example/dir/')
+  })
+
+  test('returns dirname for html files', () => {
+    expect(getHtmlDirnameForRelativeUrl('/example/dir/index.html')).toBe(
+      '/example/dir',
+    )
+  })
+
+  test('preserves root path', () => {
+    expect(getHtmlDirnameForRelativeUrl('/')).toBe('/')
+  })
+
+  test('resolves relative script from trailing slash directory', () => {
+    const preTransformUrl = path.posix.join(
+      '/',
+      getHtmlDirnameForRelativeUrl('/example/dir/'),
+      './filename.js',
+    )
+
+    expect(preTransformUrl).toBe('/example/dir/filename.js')
+  })
+})
diff --git a/packages/vite/src/node/server/middlewares/indexHtml.ts b/packages/vite/src/node/server/middlewares/indexHtml.ts
index 0e9c48518cac45..ea6b31f810f9e5 100644
--- a/packages/vite/src/node/server/middlewares/indexHtml.ts
+++ b/packages/vite/src/node/server/middlewares/indexHtml.ts
@@ -128,6 +128,10 @@ function isBareRelative(url: string) {
   return wordCharRE.test(url[0]) && !url.includes(':')
 }
 
+export function getHtmlDirnameForRelativeUrl(htmlPath: string): string {
+  return htmlPath.endsWith('/') ? htmlPath : path.posix.dirname(htmlPath)
+}
+
 const processNodeUrl = (
   url: string,
   useSrcSetReplacer: boolean,
@@ -165,7 +169,7 @@ const processNodeUrl = (
       } else if (url[0] === '.' || isBareRelative(url)) {
         preTransformUrl = path.posix.join(
           config.base,
-          path.posix.dirname(htmlPath),
+          getHtmlDirnameForRelativeUrl(htmlPath),
           url,
         )
       }