microsoft / microsoft/TypeScript
Polymorphic TypedArray methods return wrong type in subclasses
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Bug
Domain: lib.d.ts
- Dominant language
- Go
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Description
TypeScript Version: 4.0.0-dev.20200519
Search Terms:
typedarray subarray polymorphic
Code
class Buf extends Uint8Array {
foo() {}
}
new Buf(10).subarray().foo()
Expected behavior:
No error.
Actual behavior:
error TS2339: Property 'foo' does not exist on type 'Uint8Array'.
Playground Link: Playground Link
Related Issues:
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the provided Buf and Uint8Array example in the linked TypeScript Playground with the reported compiler version, then trace the TypedArray method type definitions or checker behavior involved. Done means the subclass's subarray() result permits foo() without TS2339 while preserving the existing TypedArray behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 45/100