5.9.0-beta - Type 'Buffer<ArrayBuffer>' is not assignable to type 'ArrayBuffer'

[maschwenk]

🔎 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

[jakebailey]

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]

Based on a private Discord discussion, this appears to be intentional, though I am curious if this should be flagging with @types/node 20.19.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]

#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]

The quirk of the array buffer view (TypedArray/DataView) interfaces being assignable to ArrayBuffer was a complete accident previously. Mistaking array buffer views for ArrayBuffers is a very common mishap, and one that the checker was previously blind to.

The divergence between the ArrayBuffer and array buffer view interfaces has existed since TS5.7, but only previously applied if targeting es2024+. Since #60150, it now applies universally.

[petamoriken]

Node.js's Buffer does NOT inherit from ArrayBuffer, but rather inherits from Uint8Array, so I think the problem is due to incorrect usage in the first place.

const test: Uint8Array<ArrayBuffer> = Buffer.from('test', 'utf-8');

[maschwenk]

Thanks all! Appreciate all that context!