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keyof object is number instead of string #41669
Description
TypeScript Version: 4.1.2 (actually all versions 3.3.3 - 4.1.2)
Search Terms:
keyof declared object is not only string, keyof object type, keyof declared key, keyof
Code
type GenericObject = { [key: string]: any };
type GenericKeyType = keyof GenericObject;Expected behavior:
GenericKeyType should be of type string
Actual behavior:
GenericKeyType is number | string
Playground Link:
https://www.typescriptlang.org/play?#code/C4TwDgpgBA4hB2EBOBLAxgeQEYCsJuCgF4oBvKAbQGsIQAuKAZ2FXgHMBdBgQ3hCgC+AbgBQI0JFgJk6ANK0AKuGgkaIAPYAzKYlSZc+YEKA
Related Issues:
Didn't find anything.
Activity
MartinJohns commentedon Nov 24, 2020
Duplicate of #39543. Used search terms:
keyof index numberExE-Boss commentedon Nov 24, 2020
Arguably, now that we have #40336 and #40598,
keyofshould report`${number}`for numeric index signatures.eek commentedon Nov 24, 2020
Thanks for the link to #39543 Martin Johns (@MartinJohns), but I still think this is a bug.
I'm saying it's a bug because I'm explicitly saying that
GenericObjectmust have onlystringkeys, and I've seen the reply saying it's by design decisions ofkeyofto be able to allowstring | number | symbolfrom here.But I think explicit types should be respected. Not to mention there's also an inconsistency between:
and
Playground link here
And I don't think there's any difference between:
[key: string]and[key in string]// sure, theinis meant for other usages but should still be the same.MartinJohns commentedon Nov 24, 2020
Radu-Sebastian Amarie (@eek) But it's not a bug, it's a design decision. One you probably disagree with, but nonetheless not a bug.
Different syntaxes are for different features. Consistency is not a desirable goal for something like this.
eek commentedon Nov 24, 2020
But both the variants report the exact same type for
GenericObject:How can then one
keyofreport onlystringand one reportstring | number?RyanCavanaugh commentedon Dec 1, 2020
This is the intended behavior in all cases.