11 replies

Unexpected Type Check Result in TypeScript

Isn't this a source of errors?

type A = { a?: string | undefined }
type Json = { [K in string]: string }
type Check = A extends Json ? true : false // true while I expected false

type A = { a?: string | undefined }
type Json = { [K in string]: string }
type Check = A extends Json ? true : false // true while I expected false

type A = { a?: string | undefined }
type Json = { [K in string]: string }
type Check = A extends Json ? true : false // true while I expected false

type A = { a?: string | undefined }
type Json = { [K in string]: string }
type Check = A extends Json ? true : false // true while I expected false