Typescript not respecting components defaultProps-CodePudding

I'm having trouble figuring out what's going wrong here:

export type PackageLanguage = "de" | "en";
export interface ICookieConsentProps {
    language?: PackageLanguage ;
}

function CookieConsent({ language }: ICookieConsentProps) {
    useEffect(() => {
        LanguageHelper.setLanguageFile(language || "en"); <--- PROBLEM HERE !
    }, [language]);

    return <div className="cc__gimme-cookies"></div>;
}

CookieConsent.defaultProps = {
    language: "en",
} as Partial<ICookieConsentProps>;

I'd like to use the language property in some function. Why does TypeScript ignore the defaultProps I've set for the language prop and want's me to check for undefined?

LanguageHelper.setLanguageFile(language); Argument of type 'PackageLanguage | undefined' is not assignable to parameter of type 'PackageLanguage'. Type 'undefined' is not assignable to type 'PackageLanguage'.ts(2345)

LanguageHelper.setLanguageFile(language || "en"); This works fine but is kinda redundant, since I defined defaultProps.

Thanks for any advice in advance!

Kind Regards, Andreas | asdf1414

CodePudding user response：

Because language is typed as optional so conceivably could be undefined.

You could look at combining Pick and Required utility functions to get the result you need.

export type PackageLanguage = "de" | "en";
export interface ICookieConsentProps {
    language?: PackageLanguage;
    otherProp: string;
    propNotInterestedIn: string;
}

type Props = Pick<ICookieConsentProps, 'language' | 'otherProp'>

function CookieConsent({ language }: Required<Props>) {
    useEffect(() => {
        LanguageHelper.setLanguageFile(language || "en"); <--- PROBLEM HERE !
    }, [language]);

    return <div className="cc__gimme-cookies"></div>;
}

CookieConsent.defaultProps = {
    language: "en",
    otherProp: "another prop"
} as Required<Props>;