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string: value interface not assignable to Record<string,unknown> #50087
Description
Activity
This is working as intended. Interface types don't get implicit index signatures as per #15300. The behavior where
{[k: string]: unknown}is treated more strictly than{[k: string]: any}was implemented in #30637, released with TS3.5, and was a documented breaking change.Okay, looks like for my use case, I should be using a type alias instead of an Interface, and (i cut this from the reproduction) instead of extending the interface, I need to intersect two type aliases.
Thanks for your help 😄Joe Calzaretta (@jcalz) we're trying to upgrade from typescript 4.3.5 to 4.6.4 and are now receiving this error.
Previously an interface like below would allow an interface to be passed in as the generic:
export interface IIntegration< T extends Record<symbol, unknown> = Record<symbol, unknown> > { type: IntegrationType; data: T; }If this has been a breaking change since 3.5 I'm at a loss as to why this would be happening now?
Reacted by chengfeng- locked as resolved and limited conversation to collaborators
on Oct 22, 2025
Bug Report
🔎 Search Terms
unknown record
Index signature
🕗 Version & Regression Information
Bug initially found in v4.7.4
Oldest found version with bug v3.5.1 in typescript playground
Bug found in nightly version v4.8.0-dev.20220728
⏯ Playground Link
Playground link with relevant code
💻 Code
🙁 Actual behavior
OldProps type is not assignable to NewProps.
Typescript returns the following error:
Error is consistent with old style record syntax.
Error is consistent if OldProps["name"] type is
stringoranyError not found if NewProps = Record<string, any>;
Error also not found if
[key:string]:[whatever type]is added to OldProps (triggers different expected error if type conflicts with name).🙂 Expected behavior
OldProps type is assignable to NewProps.