dynamically-typing-arguments.ts

const CommonTranslations = {
  COMMON_SUBMIT: "SUBMIT",
  COMMON_WELCOME: "WELCOME {{username}}",
} as const;

const StartPageTranslations = {
  START_PAGE_TITLE: "Startpage",
  START_PAGE_ERROR: "Error: {{error}}",
} as const;

type GetParamKeys<TTranslation extends string> = TTranslation extends ""
  ? []
  : TTranslation extends `${string}{{${infer Param}}}${infer Tail}`
  ? [Param, ...GetParamKeys<Tail>]
  : [];

const constTranslate = <
  TTranslations extends Record<string, string>,
  TKey extends keyof TTranslations,
  TParamKeys extends string[] = GetParamKeys<TTranslations[TKey]>,
>(
  translations: TTranslations,
  key: TKey,
  ...args: TParamKeys extends []
    ? []
    : [params: Record<TParamKeys[number], string>]
) => {
  const translation = translations[key];
  const params: any = args[0] || {};
  return translation.replace(/{(\w+)}/g, (_, key) => params[key]);
};

const typeTranslate = <
  T extends Record<string, string>,
  TParamKeys extends string[] = GetParamKeys<T[keyof T]>,
>(
  key: keyof T,
  ...args: TParamKeys extends []
    ? []
    : [params: Record<TParamKeys[number], string>]
) => {
  console.log(key, args);
};

// This works as it should.
constTranslate(CommonTranslations, "COMMON_WELCOME", { username: "Jan" });

// This works as it should.
constTranslate(StartPageTranslations, "START_PAGE_TITLE");

// This errors as it should.
constTranslate(CommonTranslations, "COMMON_WELCOME");

// This should give an error, but doesn't.
typeTranslate<typeof CommonTranslations>("COMMON_WELCOME");

// This works as it should.
typeTranslate<typeof StartPageTranslations>("START_PAGE_TITLE");

// This works as it should.
typeTranslate<typeof CommonTranslations>("COMMON_WELCOME", { username: "Jan" });