TS2322: Type 'string' is not assignable to type 'never-CodePudding

I have got error TS2322: Type 'string' is not assignable to type 'never'. in result[key] = forms.${key};

and don't understand how i can fix it. (without prefix everything is ok). Why typescript considers result[key] as never?

export const InitialState = {
  login: {
    login: '',
    password: '',
    accept_terms: false,
  },
  forgot: {
    login: '',
    password: '',
  },
};

type FormsKey = keyof typeof InitialState;

type FormsMap = {
  [K in FormsKey]: `forms.${K}`
};

const keys = Object.keys(InitialState) as FormsKey[];
const forms: FormsMap = keys.reduce<FormsMap>((result, key) => {
  result[key] = `forms.${key}`;
  return result;
}, {} as FormsMap);

export default forms;

CodePudding user response：

Because of const forms: FormsMap = keys.reduce<FormsMap>((result, key) => { typescript undesturd result[key] as a undefined possibility, e.g. if you find an unknow key , thats return never, if you have a defined explicit keys, you should create a type or enum for match for this key. Otherise I suggest you avoid set value in array, insteread you use an Map type for this.

CodePudding user response：

export const InitialState = {
  login: {
    login: '',
    password: '',
    accept_terms: false,
  },
  forgot: {
    login: '',
    password: '',
  },
}

type FormsMap<T> = {
  [K in keyof T]: K extends string ? `forms.${K}` : never
}

const getForms = <T>(state: T) => {
  const result: Record<string, any> = {}
  Object.entries(state).forEach(([key]) => {
    result[key] = `forms.${key}`
  })
  return result as FormsMap<T>
}

const forms = getForms(InitialState)
// type forms = {
//   forgot: "forms.forgot"
//   login: "forms.login"
// }

export default forms