TypeScript：如何扩展这种类似的类型？

Question

How can I extend the IUnitedStatesAddress to IUnitedStatesWithTerritoryAddress without repeating myself? The only difference is that IUnitedStatesWithTerritoryAddress has TUnitedStatesTerritoryAbbreviation added to the state field.

// TypeScript Type: United States Address
export interface IUnitedStatesAddress {
  apartmentSuite: string;
  street: string;
  city: string;
  state: TUnitedStatesStateAbbreviation;
  zipCode: string;
  county: TUnitedStatesCounty;
  country: string;
}

// TypeScript Type: United States With Territory Address
export interface IUnitedStatesWithTerritoryAddress {
  apartmentSuite: string;
  street: string;
  city: string;
  state: TUnitedStatesStateAbbreviation | TUnitedStatesTerritoryAbbreviation;
  zipCode: string;
  county: TUnitedStatesCounty;
  country: string;
}

Answer 1

One thing I'm pretty sure of is that you can have a base interface (not to be exported) and extend it with your two cases:

interface IUnitedStates {
  apartmentSuite: string;
  street: string;
  city: string;
  zipCode: string;
  county: TUnitedStatesCounty;
  country: string;
}

export interface IUnitedStatesAddress extends IUnitedStates {
  state: TUnitedStatesStateAbbreviation;
}

export interface IUnitedStatesWithTerritoryAddress extends IUnitedStates {
  state: TUnitedStatesStateAbbreviation | TUnitedStatesTerritoryAbbreviation;
}