Reducer helper for convenient reducer creation

reducer_helper.ts

export interface Action {
  type: string;
}

export type CreateReducerReducer<S, A> = (state: S, action: A) => S;

export type CreateReducerComponents<S, A> = Record<
  string,
  CreateReducerReducer<S, A>
>;

export const createReducer = <S, A extends Action>(
  components: CreateReducerComponents<S, A>,
  initialState: S
) => (state: S = initialState, action: A) =>
  components.hasOwnProperty(action.type)
    ? components[action.type](state, action)
    : state;
  

/*
  Usage:
  
  export const someReducer = createReducer<State, Action>(
    {
      [ActionTypes.SOME_ACTION]: (state, action) => {
        // ...
      }
    },
    initialState
  }
*/