From f2ca33ee1d14c27de984a81d2c2d08cec301519f Mon Sep 17 00:00:00 2001
From: Harshit <106448130+harshit-d3v@users.noreply.github.com>
Date: Thu, 17 Sep 2026 00:55:46 +0530
Subject: [PATCH] fix(jsdom): keep Blob bytes on jsdom 28+

jsdom 28 renamed the private `_buffer` field to `_bytes`, so
`makeCompatBlob` read `undefined` and every Blob or File used as a
request body arrived as the string "undefined".
---
 packages/vitest/src/integrations/env/jsdom.ts | 5 +++--
 test/unit/test/environments/jsdom.spec.ts     | 7 +++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/packages/vitest/src/integrations/env/jsdom.ts b/packages/vitest/src/integrations/env/jsdom.ts
index b37232883eb9..ffa661180d86 100644
--- a/packages/vitest/src/integrations/env/jsdom.ts
+++ b/packages/vitest/src/integrations/env/jsdom.ts
@@ -321,8 +321,9 @@ function createCompatUtils(window: DOMWindow): CompatUtils {
       return nodeFormData
     },
     makeCompatBlob(blob: Blob) {
-      const buffer = (blob as any)[implSymbol]._buffer
-      return new NodeBlob_([buffer], { type: blob.type })
+      const impl = (blob as any)[implSymbol]
+      // jsdom 28 renamed `_buffer` to `_bytes`
+      return new NodeBlob_([impl._bytes ?? impl._buffer], { type: blob.type })
     },
   }
   return utils
diff --git a/test/unit/test/environments/jsdom.spec.ts b/test/unit/test/environments/jsdom.spec.ts
index bac68eea1918..b61a0af842db 100644
--- a/test/unit/test/environments/jsdom.spec.ts
+++ b/test/unit/test/environments/jsdom.spec.ts
@@ -182,6 +182,13 @@ describe('FormData', () => {
 
     expect(retrievedBlob).toBeInstanceOf(File)
   })
+
+  test('keeps Blob bytes when used as a Request body', async () => {
+    const blob = new Blob(['hello world'], { type: 'text/plain' })
+    const request = new Request('http://localhost/', { method: 'POST', body: blob })
+
+    expect(await request.text()).toBe('hello world')
+  })
 })
 
 test('DOM APIs accept AbortController', () => {