With TypeScript 5.7 getData returns ArrayBufferLike instead of ArrayBuffer

[Scarabol]

Thank you all for this great library! I appreciate using it in my project. I just tried to update my TypeScript version from 5.6.3 to 5.7.2.

Starting with Typescript 5.7 typed arrays become generic. See:

• https://devblogs.microsoft.com/typescript/announcing-typescript-5-7/#support-for---target-es2024-and---lib-es2024
• Make typed arrays generic over ArrayBufferLike microsoft/TypeScript#59417

This affects for example the type definition of Uint8ArrayWriter

Previously with TypeScript 5.6.3 the following code typed data as ArrayBuffer, but starting with TypeScript > 5.7 data has type ArrayBufferLike.

// TypeScript < 5.7
const data: ArrayBuffer = await entry.getData(new Uint8ArrayWriter());
// TypeScript >= 5.7
const data: ArrayBufferLike = await entry.getData(new Uint8ArrayWriter());

My tsconfig compiler target is and has been set to ES2021.

I'm not sure how this is solved properly. My guess would be to add generic type explicitly to all TypedArrays usages, since they use Uint8Array (Example) actually. Effectively changing type definition here into this:

export class Uint8ArrayWriter extends Writer<Uint8Array<ArrayBuffer>> { }

What do you think?

[gildas-lormeau]

Thank for the info. Actually, I don't use TS for development and I was not aware of this issue. I wonder how to deal with that. I guess somehow I would need to publish 2 index.d.ts files?

[UnsungHero97]

I don't think it's necessary to publish 2 index.d.ts files. I don't see any uses of SharedArrayBuffer in the codebase so I think @Scarabol's suggestion is probably the way to do it, here's a pull request for that: #561

However, I'm not totally sure how this impacts TypeScript versions below 5.7.

[gildas-lormeau]

I accepted the PR, we'll see if it's a problem :p

[gildas-lormeau]

Unfortunately, I've reverted the commit because Angular 18 is depending on a older version of TypeScript, see #563.

[UnsungHero97]

I'll try to spend some time this week to figure this out.

[gildas-lormeau]

Thanks! I wonder if waiting would be the easiest solution. It seems that this problem doesn't really bother developers who use TS 5.7+ today.

[gildas-lormeau]

Actually, I'm probably wrong. For the record, ChatGPT suggests these fixes:

1. replace Uint8Array with Uint8Array<ArrayBufferLike>, or
2. add a new CompatibleUint8Array type to handle the old and new syntax, i.e. type CompatibleUint8Array = Uint8Array extends Uint8Array<infer T> ? Uint8Array<T> : Uint8Array;

I have some doubts regarding the first suggestion. The second one is interesting, I'll try to test it.

EDIT:

None of these suggestions actually work in https://www.typescriptlang.org/play/. However ChatGPT is now saying me that I shouldn't need to change anything in fact...

EDIT 2:

The solution below seems to work.

type CompatibleUint8Array = 
  Uint8Array extends { new (...args: any[]): infer U } 
    ? U 
    : Uint8Array;

EDIT 3:
Indeed, the code below does not trigger any error.

type CompatibleUint8Array = 
  Uint8Array extends { new (...args: any[]): infer U } 
    ? U 
    : Uint8Array;

function test(val: CompatibleUint8Array): void {
  console.log(val);
}

• in TS < 5.7

const val:Uint8Array = new Uint8Array([1, 2, 3]);
test(val);

• in TS 5.7+

const val:Uint8Array<ArrayBufferLike> = new Uint8Array([1, 2, 3]);
test(val);

[gildas-lormeau]

This does not work actually.

The code below should not trigger an error in TS 5.7+ but it does.

type CompatibleUint8Array = 
  Uint8Array extends { new (...args: any[] ): infer U } 
    ? U 
    : Uint16Array;

function test(val: CompatibleUint8Array): void {
  console.log(val);
}

const val:Uint8Array = new Uint8Array([1, 2, 3]);
test(val);

[gildas-lormeau]

I'm wondering if it's really an issue. I mean that the code below runs fine in the TS playground with TS 5.7+. @Scarabol, any thoughts?

function test(val: Uint8Array): void {
  console.log(val);
}

const val:Uint8Array = new Uint8Array([1, 2, 3]);
test(val);

const val2:Uint8Array<ArrayBufferLike> = new Uint8Array([1, 2, 3]);
test(val2);