typed-constructors.ts

# https://stackoverflow.com/questions/67341992/constructor-with-return-generic-type-based-on-param-enum-ts2322/67376400#67376400

enum Enum {
  one = 'one',
  two = 'two',
}

type Type1 = {
  field: typeof Enum.one;
  anotherField: number;
};

type Type2 = {
  field: typeof Enum.two;
  someAnotherField: number;
};

type TypeN = Type1 | Type2;

type ConstructorN<T> = () => Extract<
  TypeN,
  {
    field: T;
  }
>;

type Constructors = {
  [T in Enum]: ConstructorN<T>;
};

let constructors: Constructors = {
  [Enum.one]: () => {
    let obj: Type1 = {
      field: Enum.one,
      anotherField: 1,
    };
    return obj;
  },
  [Enum.two]: () => {
    let obj: Type2 = {
      field: Enum.two,
      someAnotherField: 2,
    };
    return obj;
  },
};

console.log(constructors[Enum.one]())
// { field: 'one', anotherField: 1 }
  
console.log(constructors[Enum.two]())
// { field: 'two', someAnotherField: 2 }