Correct TypeScript Type for thunk dispatch?

Question

I have an asynchronous redux action and so am using the thunk middleware.

I have mapStateToProps, mapDispatchToProps and connect functions for a component as follows:

const mapStateToProps = (store: IApplicationState) => {
  return {
    loading: store.products.loading,
    products: store.products.products
  };
};
const mapDispatchToProps = (dispatch: any) => {
  return {
    getAllProducts: () => dispatch(getAllProducts())
  };
};
export default connect(
  mapStateToProps,
  mapDispatchToProps
)(ProductsPage);

This all works but I wondered if is possible to replace the any type on the dispatch parameter in mapDispatchToProps?

I tried ThunkDispatch<IApplicationState, void, Action> but get the following TypeScript error on the connect function:

Argument of type 'typeof ProductsPage' is not assignable to parameter of type 'ComponentType<Matching<{ loading: boolean; products: IProduct[]; } & { getAllProducts: () => Promise<void>; }, IProps>>'.
  Type 'typeof ProductsPage' is not assignable to type 'ComponentClass<Matching<{ loading: boolean; products: IProduct[]; } & { getAllProducts: () => Promise<void>; }, IProps>, any>'.
    Types of property 'getDerivedStateFromProps' are incompatible.
      Type '(props: IProps, state: IState) => { products: IProduct[]; search: string; }' is not assignable to type 'GetDerivedStateFromProps<Matching<{ loading: boolean; products: IProduct[]; } & { getAllProducts: () => Promise<void>; }, IProps>, any>'.
        Types of parameters 'props' and 'nextProps' are incompatible.
          Type 'Readonly<Matching<{ loading: boolean; products: IProduct[]; } & { getAllProducts: () => Promise<void>; }, IProps>>' is not assignable to type 'IProps'.
            Types of property 'getAllProducts' are incompatible.
              Type '() => Promise<void>' is not assignable to type '() => (dispatch: Dispatch<AnyAction>) => Promise<void>'.
                Type 'Promise<void>' is not assignable to type '(dispatch: Dispatch<AnyAction>) => Promise<void>'.
                  Type 'Promise<void>' provides no match for the signature '(dispatch: Dispatch<AnyAction>): Promise<void>'.

Is it possible to replace the any type on the dispatch parameter in mapDispatchToProps?

Answer 1

This setup works very well for me:

// store.ts
//...
export type TAppState = ReturnType<typeof rootReducer>;
export type TDispatch = ThunkDispatch<TAppState, void, AnyAction>;
export type TStore = Store<TAppState, AnyAction> & { dispatch: TDispatch };
export type TGetState = () => TAppState;
//...
const store: TStore = createStore(
  rootReducer,
  composeEnhancers(applyMiddleware(...middleware), ...enhancers)
);
export default store;

Where rootReducer on my setup looks like this const rootReducer = createRootReducer(history);

// createRootReducer.ts
import { combineReducers, Reducer, AnyAction } from 'redux';
import { History } from 'history';
import {
  connectRouter,
  RouterState,
  LocationChangeAction,
} from 'connected-react-router';
// ... here imports of reducers
type TAction = AnyAction & LocationChangeAction<any>;

export type TRootReducer = Reducer<
  {
    // ... here types of the reducer data slices
    router: RouterState;
  },
  TAction
>;
const createRootReducer = (history: History): TRootReducer =>
  combineReducers({
    // ... here actual inserting imported reducers
    router: connectRouter(history),
  });

export default createRootReducer;

Then in connected component

import { connect } from 'react-redux';
import Add, { IProps } from './Add'; // Component
import { TDispatch, TAppState } from '../../store';

type TStateProps = Pick<
  IProps,
  'title' | 'data' | 'loading'
>;
const mapStateToProps = (
  state: TAppState,
): TStateProps => {
    // ... here you have typed state :)
    // and return the TStateProps object as required
    return {
      loading: state.someReducer.loading,
      //...
    }
}

type TDispatchProps = Pick<IProps,  'onSave'>;
const mapDispatchToProps = (
  dispatch: TDispatch,
): TDispatchProps => {
   // here you  have typed dispatch now
   // return the TDispatchProps object as required
   return {
    onSave: (): void => {
      dispatch(saveEntry()).then(() => {
        backButton();
      });
    },
   }
}

As for the thunk actions I do as follows

// this is a return type of the thunk
type TPromise = Promise<ISaveTaskResponse | Error>;

export const saveEntry = (): ThunkAction<
  TPromise, // thunk return type
  TAppState, // state type
  any, // extra argument, (not used)
  ISaveEntryAction // action type
> => (dispatch: TDispatch, getState: TGetState): TPromise => {
  // use getState
  // dispatch start saveEntry action
  // make async call
  return Axios.post('/some/endpoint', {}, {})
    .then((results: { data: ISaveTaskResponse; }): Promise<ISaveTaskResponse> => {
      // get results
      // you can dispatch finish saveEntry action
      return Promise.resolve(data);
    })
    .catch((error: Error): Promise<Error> => {
      // you can dispatch an error saveEntry action
      return Promise.reject(error);
    });
};