fix(jsdom): fix Request with Blob body on jsdom 28+

[harshit-d3v]

Description

Under environment: 'jsdom', a Blob used as a request body arrives as the string undefined. makeCompatBlob reads jsdom's private _buffer field, which jsdom 28 renamed to _bytes. Reads whichever exists so both halves of the * peer range keep working.

Adds a test that fails without the change: a Blob used as a Request body. The existing supports Blob test uses an empty blob and only checks toBeInstanceOf, so it never saw the content go missing.

The related Node 24 File/FormData breakage (#9135) is a separate issue with a different cause (undici 7 reading File from the global) and will be a follow-up PR.

Resolves #11294

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time.
• Ideally, include a test that fails without this PR but passes with it.
• Please, don't make changes to pnpm-lock.yaml unless you introduce a new test example.

Tests

• Run the tests with pnpm test:ci.

I used Claude to help find and fix this. I reproduced it myself and reviewed the change.

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[Copilot]

🟢 Approval recommended

The fix and regression tests address the reported issue with no unresolved review comments.

Pull request overview

Fixes Blob and File request bodies under jsdom 28+ by supporting its renamed internal byte field.

Changes:

• Supports both _bytes and legacy _buffer.
• Adds regression tests for Blob and multipart File bodies.

File summaries

File	Description
test/unit/test/environments/jsdom.spec.ts	Adds request-body regression tests.
packages/vitest/src/integrations/env/jsdom.ts	Adds compatibility for both jsdom byte-field names.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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[hi-ogawa]

Can you check CI fali?

[harshit-d3v]

Pushed a fix. undici 7 on Node 24 resolves File from the global inside FormData.append, and the jsdom env swaps that global, so the Node blob got wrapped in a jsdom File. Now wraps it in Node's File first. Unit jobs are green. The two remaining failures are browser mode (mocking.test.ts importOriginal, looks like #11251, and bail-out.test.ts), could you re-run those?

[hi-ogawa]

iirc there was something tricky about Node 24 File and FormData. Could these be relevant?

• fix: fix request.body hanging on node v24.6.0 and up #9151
• .formData()/.arrayBuffer() promise never resolves when using jsdom with File/Blob in FormData on Node 24 #9135

[harshit-d3v]

Yes, that's it. undici 7 dropped the node:buffer imports (nodejs/undici#4362, Node 24.6+), so FormData.append and the multipart parser read File from the global at call time, and in this env that global is jsdom's File.

Pushed the other half too. The parser builds each part with new File from the global and then brand checks it, so formData() threw under threads and forks. Now Node's File is put back on the global for the duration of formData() on Request and Response, and the result is converted to jsdom FormData/File so instanceof still works in tests. Restored on teardown. That covers #9135. Tested on Node 22 and 24.21 locally.

[hi-ogawa]

Aren't the two issues independent? Should we split PR?

[harshit-d3v]

You're right, they're independent: #11294 is the jsdom 28 _buffer rename (any Node), #9135 is undici 7 reading File from the global on Node 24.6+ (any jsdom). I'd normally split, but the repo limits outside contributors to one open PR, so I bundled them to avoid opening a second. They're all in the same few lines of jsdom.ts. Happy to drop the Node 24 commits and open a separate PR for #9135 after this merges if you'd prefer that.

[hi-ogawa]

split pls

[harshit-d3v]

Done. This PR is now just #11294: the jsdom 28 _buffer to _bytes rename, plus one test for a Blob request body. The Node 24 File/FormData work (#9135) is off on a branch and I'll open it as a separate PR once this one lands.

[harshit-d3v]

The only red job is the #11251 browser-mode mock flake again (mocking virtual module without importOriginal ... (playwright), the "failed to fetch dynamically imported module" race). Not related to this change, the jsdom test passes. Could you re-run that job?

[hi-ogawa]

The existing tests in test/unit/test/environments/jsdom.spec.ts use an empty new Blob() and only assert toBeInstanceOf (from #11294)

Where is this? You seem to suggest there's already a test case to expand.

[harshit-d3v]

it's the supports Blob test in test/unit/test/environments/jsdom.spec.ts:160:

const data = new Blob()
form.set(key, data)
const retrievedBlob = form.get(key)
expect(retrievedBlob).toBeInstanceOf(Blob)

that one uses an empty blob and only checks the type, so it never noticed the bytes were gone. the test i added sends a real blob as a request body and reads it back, thats the case that was broken.

[hi-ogawa]

should supports Blob exercise something with non-empty blob? I didn't get the nuance of why you bring that test in the issue if it's not relevant for this PR.

[harshit-d3v]

right, that was more of a side note than something this PR needs.

making supports Blob non-empty wouldn't catch this one either. that test goes through form.get(), which hands back jsdom's own Blob and never touches the compat conversion. the broken path is only when a Blob is used as a Request body, which is what my new test covers.

i mentioned it in the issue just to explain why the regression wasn't caught before. i can drop that line if it reads as if the old test should change.

[hi-ogawa]

What about the coverage of new Blob(['hello']).text()?

[harshit-d3v]

new Blob(['hello']).text() goes through jsdom's own Blob and returns 'hello' fine, with or without this fix. same for .arrayBuffer(). those never hit the compat conversion.

the break only shows when the blob is passed to Node's fetch/Request, which is the path makeCompatBlob is on. i just checked on the current main build: .text() and .arrayBuffer() pass, only the Request-body case fails. so a .text() test wouldn't catch this one, that's why the test sends the blob as a request body.