formatString() TypeScript type specifies Array as a return value

[peterbasar]

Hello, thanks for making this package. I enjoy using it.
However, I encountered a potential issue while using it with TypeScript.
It seems that formatString() return type specifies an Array as well as string.
Shouldn't it only be a string? Since even docs specify that it returns a string.

formatString() - formats the input string and returns a new string, replacing its placeholders with the other arguments strings

See the location of the type and commit in question:
8a700b2#r133591646

Seems that this the potential issue has been introduced in:
f3f7385

[stefalda]

Hi, I have to review the code, because it seems to me that that change was required to be able to intermix JSX code in the returned string, I don't remember if the result is an array and so the tpe definition had to be modified ...

[peterbasar]

Do you think it is a good decision to have both JSX and string formatting for 1 function?
It generally doesn't matter if the output is used directly in the renderer. But when the formatString output is used as an function argument there will have to be additional checking on every use.

[stefalda]

The JSX interpolation wasn't an option at start, it was added in a second time... but if we create a separate function we break existing uses..

[michaeltnguyen]

It's a hack, but you can override this behavior in your project by extending the LocalizedStringsMethods type.

// copied from type definition
// https://github.com/stefalda/react-localization/blob/master/lib/LocalizedStrings.d.ts
type Formatted = number | string | JSX.Element;
type FormatObject<U extends Formatted> = { [key: string]: U };

interface FixedLocalizedStringsMethods extends LocalizedStringsMethods {
  formatString<T extends Formatted>(
    str: string,
    ...values: Array<T | FormatObject<T>>
  ): string;
}

// now strings.formatString just returns a string
export type strings = FixedLocalizedStringsMethods & ILocalizedStrings;