How to use async methods inside Redux actions using Redux-Thunk

Gustavo Gonzalez
Aug 30, 2018 · 4 min read
Redux-Thunk Flow

If you are using Redux, probably you noticed that actions only can return plain objects, something like:

{ type: HERE_THE_ACTION_TYPE, anObject }

If we try to return any other thing like for example a function, the browser will nicely remember it with a message:

Action must be plain object

In the message, Redux is telling us the solution: Use custom middleware for async actions

This article will help us to prevent the error using Redux-Thunk.

First steps

npx create-react-app demo-react-thunk
cd demo-react-thunk
yarn add redux react-redux redux-thunk

The good stuff

  • An action: it will fetch the user data
  • A reducer: to put the data in the global state
  • An store: to save the global state
  • A component: to show the data

The action

export const fetchUsers = () => {
return dispatch => {
.then(response => response.json())
.then(json => dispatch({ type: 'FETCH_ALL_USERS', json }))

What are we doing there?

Instead of returning a plain object we are returning a function that expects the dispatch method as parameter, the function is asking for some dummy data using service, transform the response to json and then return the plain object action using dispatch. For details about dispatch method, please read the official redux docs

The reducer

import { combineReducers } from 'redux';const user = (state = { users: [] }, action) => {
switch (action.type) {
return {
users: action.json
return state;
export default combineReducers({

The store

import { applyMiddleware, createStore } from 'redux';
import thunkMiddleware from 'redux-thunk';
import rootReducer from './reducers/user';

and then we should create the store with following code:

const store = createStore(

What we are doing here, is asking our store to apply a middleware, remember the original message about using custom middleware for async actions?. The middleware in this case is Redux-Thunk that will help us to run async methods in the action.

The code for src/index.js should looks like the following

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import { Provider } from 'react-redux';
import { applyMiddleware, createStore } from 'redux';
import thunkMiddleware from 'redux-thunk';
import rootReducer from './reducers/user';
const store = createStore(
<Provider store={store}>
<App />

The component

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import { connect } from "react-redux";
import { fetchUsers } from "./actions/user"
class App extends Component {
componentDidMount() {
render() {
const { users } = this.props;
return (
<div className="App">
<header className="App-header">
<img src={logo} className="App-logo" alt="logo" />
<h1 className="App-title">Redux Thunk Demo</h1>
users.length > 0 &&
{ =>
<tr key={}>
const mapStateToProps = (state) => {
return state.user;
const mapDispatchToProps = (dispatch) => ({
fetchUsers: () => dispatch(fetchUsers())
export default connect(mapStateToProps, mapDispatchToProps)(App);

That's all folks

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