[BUG]: TypeScript throws errors when adding [key: string]: string if other properties are not of type string

[RodrigoTomeES]

[BUG]: TypeScript throws errors when adding [key: string]: string if other properties are not of type string

[MartinJohns]

This is working as intended. The type of the index signature must be at least a union including all types of the known properties. This is documented: https://www.typescriptlang.org/docs/handbook/2/objects.html#index-signatures

If you really want this, you can use an intersection type instead: { test: { url: string } } & { [key: string]: string }
But be aware that this is not sound. It's easy to still assign a string to the property test.

[fatcerberus]

To represent this type properly you'd need #17867