Ganesh Mani I'm a full-stack developer, Android application/game developer, and tech enthusiast who loves to work with current technologies in web, mobile, the IoT, machine learning, and data science.

How to build a type-safe React Redux app

6 min read 1755

How to Build a Type-Safe React Redux App

Adding a type checking feature to your React application can help you catch lots of bugs at compile time. In this tutorial, we’ll demonstrate how to build a type-safe React Redux app by examining a real-world example.

To illustrate these concepts, we’ll create a sample e-commerce app like the one shown below.

E-Commerce App E-Cart Example

E-Commerce App E-Cart Example

Completed E-Commerce App E-Cart Example

Without further ado, let’s get started!

Building a type-safe Redux app

React is a component library that we use to build the frontend of modern applications. As an application expands, it becomes increasingly difficult to manage data.

That’s where Redux comes in. Basically, Redux is a state management library that is popular in the React ecosystem. If you’re new to the concept of React Redux, I recommend reading the official docs before proceeding with this tutorial.

Let’s start by building an e-commerce application workflow. Here, we have two important domains in the wireframe: inventory and cart.

Diagram Showing Inventory and Cart Domains

We made a custom demo for .
No really. Click here to check it out.

First, we’ll create the essential Redux building blocks — namely, action creator, reducer, and store. Since we know the application domains, we’ll structure our app based on that.

Create a react application using this command:

npx create-react-app react-redux-example --template typescript

This will create a React application boilerplate with TypeScript files. Next, install the dependencies for React Redux and its types.

npm i react-redux redux redux-thunk
npm i --save-dev @types/react-redux 

The above command should install the redux and react-redux libraries, which handle the React and Redux connection. Next, install redux-thunk, which is a middleware used to handle the asynchronous data fetching in action creators.

Now it’s time to create a file structure for our Redux store.

Redux Store File Structure

The application store is structured based on the domain. You can see that all the actions, reducers, and types of the inventory domain are maintained in one folder, whereas the actions, reducers, and types of the cart domain are maintained in an another folder.

Inventory domain

Let’s start with the inventory domain. We need to create actions, reducers and types for the inventory domains. I always start with domain type because that way, I can define the structure of the specified domain at an early stage.

The type will contain the redux state, action types, and domain.

 export interface Inventory {
  id: string;
  name: string;
  price: string;
  image: string;
  description: string;
  brand?: string;
  currentInventory: number;
}
export enum InventoryActionTypes {
  FETCH_REQUEST = "@@inventory/FETCH_REQUEST",
  FETCH_SUCCESS = "@@inventory/FETCH_SUCCESS",
  FETCH_ERROR = "@@inventory/FETCH_ERROR"
}
export interface InventoryState {
  readonly loading: boolean;
  readonly data: Inventory[];
  readonly errors?: string;
}

A few notes about the code above:

  • The Inventory interface determines the specified domain data
  • The InventoryActionTypes enum determines the action types
  • The Inventory state handles the type of domain state

Now, it’s time to create an actions for the inventory store.

import { InventoryActionTypes } from "./types";
import { ActionCreator, Action, Dispatch } from "redux";
import { ThunkAction } from "redux-thunk";
import { ApplicationState } from "../index";
import inventory from "../../mockdata";

export type AppThunk = ActionCreator<
  ThunkAction<void, ApplicationState, null, Action<string>>
>;

export const fetchRequest: AppThunk = () => {
  return (dispatch: Dispatch): Action => {
    try {
      return dispatch({
        type: InventoryActionTypes.FETCH_SUCCESS,
        payload: inventory
      });
    } catch (e) {
      return dispatch({
        type: InventoryActionTypes.FETCH_ERROR
      });
    }
  };
};

First, we’ll use Redux Thunk as a middleware in the action to make API calls. What is Redux Thunk, anyway? Basically, the action creator returns an object that has action type and payload. redux-thunk turns the action into a function that makes an API call in the intermediate and returns the data by dispatching an action.

Here, we have an action, fetchRequest, which basically returns a function. That function makes an API call (here, we mocked the inventory data instead of an API call). After that, it dispatches an action.

We should also briefly mention type checking for action. Every action should be of type ActionCreator. Since we used Redux Thunk, each ActionCreator returns a function that has type ThunkAction.

If you’re new to Redux Thunk, check out the excellent documentation for an in-depth look.

The final part of the inventory store is the reducer. Let’s create that file.

import { Reducer } from "redux";
import { InventoryActionTypes, InventoryState } from "./types";
export const initialState: InventoryState = {
  data: [],
  errors: undefined,
  loading: false
};
const reducer: Reducer<InventoryState> = (state = initialState, action) => {
  switch (action.type) {
    case InventoryActionTypes.FETCH_REQUEST: {
      return { ...state, loading: true };
    }
    case InventoryActionTypes.FETCH_SUCCESS: {
      console.log("action payload", action.payload);
      return { ...state, loading: false, data: action.payload };
    }
    case InventoryActionTypes.FETCH_ERROR: {
      return { ...state, loading: false, errors: action.payload };
    }
    default: {
      return state;
    }
  }
};
export { reducer as InventoryReducer };

First, define an initial state that has a type of InventoryState.

export const initialState: InventoryState = {
  data: [],
  errors: undefined,
  loading: false
};

After that, create a reducer with a state type of InventoryState. It’s very important to define the types for each reducer because you want to identify issues at compile time rather than run time.

const reducer: Reducer<InventoryState> = (state = initialState, action) => {
  switch (action.type) {
    case InventoryActionTypes.FETCH_REQUEST: {
      return { ...state, loading: true };
    }
    case InventoryActionTypes.FETCH_SUCCESS: {
      console.log("action payload", action.payload);
      return { ...state, loading: false, data: action.payload };
    }
    case InventoryActionTypes.FETCH_ERROR: {
      return { ...state, loading: false, errors: action.payload };
    }
    default: {
      return state;
    }
  }
};

Here, we handle all the actions of the inventory domain and update the state.

Cart domain

It’s time to implement the redux functionalities for the cart. The functionalities of the cart domain are similar to those of the inventory domain.

First, create a file named types.ts and add the following code.

import { Inventory } from "../inventory/types";
export interface Cart {
  id: number;
  items: Inventory[];
}
export enum CartActionTypes {
  ADD_TO_CART = "@@cart/ADD_TO_CART",
  REMOVE_FROM_CART = "@@cart/REMOVE_FROM_CART",
  FETCH_CART_REQUEST = "@@cart/FETCH_CART_REQUEST",
  FETCH_CART_SUCCESS = "@@cart/FETCH_CART_SUCCESS",
  FETCH_CART_ERROR = "@@cart/FETCH_CART_ERROR"
}
export interface cartState {
  readonly loading: boolean;
  readonly data: Cart;
  readonly errors?: string;
}

This represents the cart domain attributes, cart action types, and cart state of Redux.

Next, create action.ts for the cart domain.

import { CartActionTypes, Cart, cartState } from "./types";
import { Inventory } from "../inventory/types";
import { ActionCreator, Action, Dispatch } from "redux";
import { ThunkAction } from "redux-thunk";
import { ApplicationState } from "../index";
export type AppThunk = ThunkAction<
  void,
  ApplicationState,
  null,
  Action<string>
>;
export const fetchCartRequest: AppThunk = () => {
  return (dispatch: Dispatch, state: ApplicationState): Action => {
    try {
      return dispatch({
        type: CartActionTypes.FETCH_CART_SUCCESS,
        payload: state.cart
      });
    } catch (e) {
      return dispatch({
        type: CartActionTypes.FETCH_CART_ERROR
      });
    }
  };
};
export const addToCart: ActionCreator<ThunkAction<
  void,
  ApplicationState,
  Inventory,
  Action<string>
>> = item => {
  return (dispatch: Dispatch): Action => {
    try {
      return dispatch({
        type: CartActionTypes.ADD_TO_CART,
        payload: item
      });
    } catch (e) {
      return dispatch({
        type: CartActionTypes.ADD_TO_CART_FAILURE,
        payload: null
      });
    }
  };
};

action.ts contains all the actions that handle the cart domain functionalities.

Here we’re using redux-thunk to make an API fetch call. We mocked it for the purpose of this tutorial, but in production, you can fetch an API inside action creators.

Finally, write the code for the cart domain reducer. Create a file, name it reducer.ts, and add the following code.

import { Reducer } from "redux";
import { CartActionTypes, cartState } from "./types";
export const initialState: cartState = {
  data: {
    id: 0,
    items: []
  },
  errors: undefined,
  loading: false
};
const reducer: Reducer<cartState> = (state = initialState, action) => {
  switch (action.type) {
    case CartActionTypes.FETCH_CART_REQUEST: {
      return { ...state, loading: true };
    }
    case CartActionTypes.FETCH_CART_SUCCESS: {
      return { ...state, loading: false, data: action.payload };
    }
    case CartActionTypes.FETCH_CART_ERROR: {
      return { ...state, loading: false, errors: action.payload };
    }
    case CartActionTypes.ADD_TO_CART: {
      return {
        errors: state.errors,
        loading: state.loading,
        data: {
          ...state.data,
          id: state.data.id,
          items: [...state.data.items, action.payload]
        }
      };
    }
    case CartActionTypes.REMOVE_FROM_CART: {
      return {
        errors: state.errors,
        loading: state.loading,
        data: {
          ...state.data,
          id: state.data.id,
          items: state.data.items.filter(item => item !== action.payload.id)
        }
      };
    }
    default: {
      return state;
    }
  }
};
export { reducer as cartReducer };

Now it’s time to configure the store for our application.

Configure store

Create a file named configureStore.ts in the root directory and add the following code.

import { Store, createStore, applyMiddleware } from "redux";
import thunk from "redux-thunk";
import { routerMiddleware } from "connected-react-router";
import { History } from "history";
import { ApplicationState, createRootReducer } from "./store";
export default function configureStore(
  history: History,
  initialState: ApplicationState
): Store<ApplicationState> {
  const store = createStore(
    createRootReducer(history),
    initialState,
    applyMiddleware(routerMiddleware(history), thunk)
  );
  return store;
}

We created a function called configureStore, which takes history, and initialState as an argument.

We need to define the type for arguments such as history and initialState. initialState should have the type of ApplicationStore, which is defined in the store. The configureStore function returns the type Store, which contains the ApplicationState.

After that, create a store that takes the root reducer, initialStore, and middlewares, which are routerMiddleware and redux-thunk here.

We’re finally done with the Redux part. Next we’ll demonstrate how to implement the components for it.

Components structure

Let’s zoom in on our components.

Redux Store Component Structure

  • HomePage handles the main page, which renders the ProductItem component
  • Navbar renders the navbar and cart items count
  • Cart contains the list items that are added to the cart

Once you know how to structure a type-safe Redux application, implementing components is fairly straightforward. Take the component part as an exercise and leave a comment below with your GitHub link.

You can find the complete source code for reference on GitHub.

What’s next?

Now that you know how to build a type-safe Redux application using React Redux, Redux, and Redux Thunk, you may notice that it takes a lot of code just to set up Redux in your application.

Fortunately, there’s a solution to this problem: Redux Toolkit. This package is designed to ease the process of implementing Redux.

Here is a quick outline of Redux toolkit:

  • configureStore() is like a wrapper of creatorStore() in Redux. It comes with some Redux dev tools out of the box, eliminating the need to set it up
  • createReducer() is a utility function that replaces the traditional reducers boilerplate in the Redux applications
  • createAction() is basically a helper function for defining Redux action types and creators
  • createSlice() is a function that automatically generates action creators and action types based on an initialState and reducer function

Summary

Adding a type check can help you avoid issues at compile time itself. For further reading, an understanding of the following concepts will help you along your type checking journey.

You come here a lot! We hope you enjoy the LogRocket blog. Could you fill out a survey about what you want us to write about?

    Which of these topics are you most interested in?
    ReactVueAngularNew frameworks
    Do you spend a lot of time reproducing errors in your apps?
    YesNo
    Which, if any, do you think would help you reproduce errors more effectively?
    A solution to see exactly what a user did to trigger an errorProactive monitoring which automatically surfaces issuesHaving a support team triage issues more efficiently
    Thanks! Interested to hear how LogRocket can improve your bug fixing processes? Leave your email:

    Full visibility into production React apps

    Debugging React applications can be difficult, especially when users experience issues that are difficult to reproduce. If you’re interested in monitoring and tracking Redux state, automatically surfacing JavaScript errors, and tracking slow network requests and component load time, try LogRocket.

    LogRocket is like a DVR for web apps, recording literally everything that happens on your React app. Instead of guessing why problems happen, you can aggregate and report on what state your application was in when an issue occurred. LogRocket also monitors your app's performance, reporting with metrics like client CPU load, client memory usage, and more.

    The LogRocket Redux middleware package adds an extra layer of visibility into your user sessions. LogRocket logs all actions and state from your Redux stores.

    Modernize how you debug your React apps — .

    Ganesh Mani I'm a full-stack developer, Android application/game developer, and tech enthusiast who loves to work with current technologies in web, mobile, the IoT, machine learning, and data science.

    2 Replies to “How to build a type-safe React Redux app”

    1. Hi, I’m a Redux maintainer.

      We have several specific recommendations that would differ from some of the patterns shown in this article:

      – You should use our new official Redux Toolkit package. It includes utilities to simplify several common Redux use cases, including store setup, defining reducers, immutable update logic, and even creating entire “slices” of state at once. In particular, all of the hand-written action types and action creators here are unnecessary, as our `createSlice` API can auto-generate those. It has a `configureStore` function that does most of the work shown in this example, and it uses Immer internally to let you write much simpler immutable update logic. It’s also already written in TypeScript, and designed to minimize the number of explicit type declarations you have to include.
      – We recommend using thunks as the default approach for async logic. Sagas are a great power tool, but most apps don’t need the overhead and complexity of sagas. In addition, sagas don’t play well with TypeScript.
      – The use of a “feature folder” structure is reasonable, but we’d actually suggest trying to use the “ducks” pattern for single-file Redux logic, as that reduces the number of files you have to deal with. This becomes even easier because `createSlice` basically gives you ducks file for free.

      Finally, note that we have a Usage with TypeScript docs page that gives instructions on how to use TS with Redux apps.

    2. Thank you so much for your valuable feedback and enhancement. i will update the article as per the suggested way in the documentation.

    Leave a Reply