Typescript + Redux + Typescript Readonly Interfaces

third-iteration-1.ts

// scaffolding
interface IPostState
  extends Readonly<{
      post: IPost | null;
      isLoading: boolean;
    }> {} // this has to be a Readonly interface as well.

// reducers
const INITIAL_STATE: IPostState = {
  post: null,
  isLoading: false,
};

function postReducer(state: IPostState = INITIAL_STATE, action): IPostState {
  switch (action.type) {
    case "FETCHED": {
      return {
        post: action.payload.post,
        isLoading: false,
      };
    }
    case "UPDATED_TITLE": {
      return {
        ...state,
        post: {
          ...state.post,
          title: action.payload.title,
        },
      };
    }
    default: {
      return state;
    }
  }
}