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5.9.0-beta - Type 'Buffer<ArrayBuffer>' is not assignable to type 'ArrayBuffer' #62109
Description
🔎 Search Terms
ArrayBuffer
Type 'Buffer' is not assignable to type 'ArrayBuffer'.`
5.9.0-beta
🕗 Version & Regression Information
https://stackblitz.com/edit/vitejs-vite-ymeftbvq?file=tsconfig.json
With @types/node set to 20.19.4 as a constant, this code below is fine in 5.8.3
const test: ArrayBuffer = Buffer.from('test', 'utf-8');errors with error TS2322: Type 'Buffer<ArrayBuffer>' is not assignable to type 'ArrayBuffer'. in 5.9.0-beta
- This changed between versions 5.8.3 and 5.9.0-beta
It appears to be fixable by switching to
const test: ArrayBuffer = Buffer.from('test', 'utf-8').buffer⏯ Playground Link
https://stackblitz.com/edit/vitejs-vite-ymeftbvq?file=tsconfig.json
🙁 Actual behavior
Failed typechecking
🙂 Expected behavior
Expected this to pass
Additional information about the issue
No response
Activity
jakebailey commentedon Jul 23, 2025
Given Buffer isn't an ArrayBuffer, I'm pretty sure this is intentional. https://nodejs.org/api/buffer.html#bufbuffer is an ArrayBuffer.
Unless I'm really missing something.
maschwenk commentedon Jul 23, 2025
Based on a private Discord discussion, this appears to be intentional, though I am curious if this should be flagging with
@types/node20.19.x. Also just curious which commit/PR changed this, I tried scanning through v5.8.3...v5.9-beta but was having trouble finding.jakebailey commentedon Jul 23, 2025
#61647 and related PRs.
All currently supported Node types pass with the last 10 versions of TS, so I would think this would behave correctly.
Renegade334 commentedon Jul 24, 2025
The quirk of the array buffer view (TypedArray/DataView) interfaces being assignable to
ArrayBufferwas a complete accident previously. Mistaking array buffer views forArrayBuffers is a very common mishap, and one that the checker was previously blind to.The divergence between the
ArrayBufferand array buffer view interfaces has existed since TS5.7, but only previously applied if targeting es2024+. Since #60150, it now applies universally.petamoriken commentedon Jul 24, 2025
Node.js's
Bufferdoes NOT inherit fromArrayBuffer, but rather inherits fromUint8Array, so I think the problem is due to incorrect usage in the first place.maschwenk commentedon Jul 24, 2025
Thanks all! Appreciate all that context!
Fix ArrayBuffer type errors with TypeScript 5.9
Fix ArrayBuffer type errors with TypeScript 5.9