Converting form data to desired types in a schema

export const RegistrationFormStruct = S.Struct({
    [RegisterFormFieldKey.Username]: S.String.pipe(
        S.nonEmpty({ message: () => MessageKey.UsernameRequired }),
        S.filter((value) =>
            value.length < 20 ? undefined : MessageKey.UsernameMaxLength,
        ),
        S.filter((value) =>
            // must not contain whitespace or non-alphanumeric characters
            /^[a-zA-Z0-9]*$/.test(value)
                ? undefined
                : MessageKey.UsernameAlphanumeric,
        ),
    ),
    [RegisterFormFieldKey.AcceptTermsAndConditions]: S.Boolean.pipe(
        S.filter((value) =>
            value ? undefined : MessageKey.TermsAndConditionsRequired,
        ),
    ),
});