TypeScript typings

action_typing.ts

type ActionTree<T> = {
  [ K in keyof T ]: {
    type: K;
    payload: T[K] extends { payload: any } ? T[K]['payload'] : never;
  };
};

type HogeActionTree = ActionTree<{
  'hoge/get': {
    payload: { id: string; };
  };
  'hoge/getList': {
    payload: null;
  };
}>;
type FooActionTree = ActionTree<{
  'foo/get': {
    payload: { id: string; };
  };
}>;

type MakeActions<T> = T extends { type: string; payload: any } ? T : T[keyof T];

type Actions<T> = T extends [...any[]]
  ? { [I in keyof T]: MakeActions<T[I]>; }[number]
  : MakeActions<T>;

type T1 = Actions<HogeActionTree>
type T2 = Actions<[HogeActionTree, FooActionTree]>
type T3 = Actions<[HogeActionTree['hoge/get'], FooActionTree]>

typeguard.ts

type TypeMaps = {
  string: string;
  number: number;
  boolean: boolean;
};

type ConstructorOrTypename = { new(...args: any[]): any } | keyof TypeMaps;

type TypeFrom<T extends ConstructorOrTypename> =
  T extends { new(...args: any[]): infer I }
    ? I
    : T extends keyof TypeMaps
      ? TypeMaps[T]
      : never;

function isType<T extends ConstructorOrTypename>(type: T) : type is TypeFrom<T> {
  return true;
}

isType(Error);
isType('string');
isType('number');