Middleware And Async Action In Redux

Introduction

In the previous article, we have learned about the multiple-reducer concept in Redux along with its implementation using the combineReducer() method. Now, in this article, we will be learning about the concept of Middleware along with its usage and Async actions in Redux.

Middleware

In Redux, middleware provides a third-party extension point between dispatching an action and handling the action off the reducer.

Action <-> Middleware <-> Dispatcher

Middleware provides a way to extend Redux with custom functionality. It is mainly used for logging, crash reporting, asynchronous requests, route handling, and many more.

The best feature of middleware is that it can be composed in a chain. You can use multiple independent third-party middlewares in a single project.

Let’s start with the implementation of Middleware using redux-logger.

So, implement it by installing it in Visual Studio Code.

npm i --save redux-logger

Now, we will be updating the previous code as below.

First, import the redux-logger after installation.

const reduxLogger = require('redux-logger')

Now, create a variable for applyMiddleware function from the Redux library.

const applyMiddleware = redux.applyMiddleware
const logger = reduxLogger.createLogger()

After that, update it in createStore as the second argument.

const store = createStore(rootReducer,applyMiddleware(logger))

The overall code looks like below.

const redux = require('redux')
const reduxLogger = require('redux-logger')
console.log("Index js in redux app")
const createStore = redux.createStore
const combineReducer = redux.combineReducers
const applyMiddleware = redux.applyMiddleware
const logger = reduxLogger.createLogger()
const LOGIN = 'LOGIN'
const USER_DETAIL = 'USER_DETAIL'
// action
function loggedIn(user, pwd) {
return {
type: LOGIN,
username: user,
password: pwd,
loggedInStatus: ""
}
}
function updateUserName(FirstName, LastName, UserName) {
return {
type: USER_DETAIL,
FirstName: FirstName,
LastName: LastName,
UserName: UserName
}
}
function callLoginApi(username, password) {
if (username === 'admin' && password === 'admin') {
return "Login Success";
} else {
return 'Invalid email and password';
}
}
const initialLoginState = {
username: "test",
password: "test",
loggedInStatus: ""
}
const initialUserState = {
FirstName: "",
LastName: "",
UserName: ""
}
const loginReducer = (state = initialLoginState, action) => {
switch (action.type) {
case LOGIN:
return {
...state,
username: action.username,
password: action.password,
loggedInStatus: callLoginApi(action.username, action.password)
}
default:
return state
}
}
const UserReducer = (state = initialUserState, action) => {
switch (action.type) {
case USER_DETAIL:
return {
...state,
FirstName: action.FirstName,
LastName: action.LastName,
UserName: action.UserName
}
default:
return state
}
}
const rootReducer = combineReducer({
login : loginReducer,
userDetail : UserReducer
})
const store = createStore(rootReducer,applyMiddleware(logger))
console.log("Initial State", store.getState())
const unsubscribe = store.subscribe(() => {})
store.dispatch(loggedIn("user", "user"))
store.dispatch(loggedIn("admin", "admin"))
store.dispatch(updateUserName("priyanka", "jain", "[email protected]"))
store.dispatch(updateUserName("test", "test", "[email protected]"))
unsubscribe()

This will display the output as below.

In the image, the output is displaying the log, stating which action is performing after the % sign.

Now, we are going to learn about Asynchronous action along with middleware.

Async Actions

In the previous article, we have seen about synchronous action, i.e., as soon as the action is dispatched, the state gets updated. But there are some scenarios when we need to update the state based on some API calls or something that takes time to execute. Then, we need to use Async Actions.

Let’s look at the demo which fetches data from API using the Redux application.

Now, for fetching data from API, we will see how to write code in the Redux application.

First of all, our state should go like this:

State = {
loading : true, // display till data load
data : [], // once data loaded it will be displayed in it
error:’’ // While calling API if any error occurs here it will be stored
}

Secondly, these actions need to be performed.

FETCH_DATA_REQUEST – Retrieve a list of data from API

FETCH_DATA_SUCCESS – When data retrieval is done successfully

FETCH_DATA_FAILURE – When there is an error while retrieving data

At last, Reducer will perform an evaluation based on actions.

CASE FETCH_DATA_REQUEST:
loading: true
CASE FETCH_DATA_SUCCESS:
loading: false,
users:data, // data returned from API
CASE FETCH_DATA_FAILURE:
loading : false,
error : error // if any error occurred by API

Now, let’s create a new JavaScript file as - asyncActionDemo.js.

const redux = require('redux')
const createStore = redux.createStore
const initialState = {
loading: false,
data: [],
error: ''
}
const FETCH_DATA_REQUEST = 'FETCH_DATA_REQUEST'
const FETCH_DATA_SUCCESS = 'FETCH_DATA_SUCCESS'
const FETCH_DATA_FAILURE = 'FETCH_DATA_FAILURE'
const fetchDataRequest = () => {
return {
type: FETCH_DATA_REQUEST
}
}
const fetchDataSuccess = data => {
return {
type: FETCH_DATA_SUCCESS,
payload: data
}
}
const fetchDataError = error => {
return {
type: FETCH_DATA_FAILURE,
payload: error
}
}
const reducer = (state = initialState, action) => {
switch (action.type) {
case FETCH_DATA_REQUEST:
return {
...state,
loading: true
}
case FETCH_DATA_SUCCESS:
return {
loading: false,
data: action.payload,
error:''
}
case FETCH_DATA_FAILURE:
return {
loading: false,
users:[],
error: action.payload
}
}
}
const store = createStore(reducer)

After the basic definition of State, Action, and Reducers, now we will need to add API calls and for that, we will need to install 2 more packages, as mentioned below.

axios

To make a request to API calls

redux-thunk

It is a standard way to define Asynchronous action creators in Redux application. It is a middleware that will be applied to the Redux store.

So first, we need to install both the packages in the terminal using the command.

npm install axios redux-thunk

After the successful installation of packages, we will import it in the JS file.

const applyMiddleware = redux.applyMiddleware
const thunkMiddleware = require('redux-thunk').default
const axios = require('axios')

and update the middleware in the store.

const store = createStore(reducer,applyMiddleware(thunkMiddleware))

Now, we will be creating a method that will call the API, but as we know, in an Action creator, only actions are returned; using thunk middleware, we have the functionality of returning a function that is not required to be pure.

In this demo, we will be using dummy API “https://jsonplaceholder.typicode.com”.

We will add an action creator containing the API call.

const fetchData = () => {
return function (dispatch) {
dispatch(fetchDataRequest())
axios.get("https://jsonplaceholder.typicode.com/users")
.then(response => {
const data = response.data.map(user => user.name)
dispatch(fetchDataSuccess(data))
})
.catch(error => {
dispatch(fetchDataError(error.message))
})
}
}

And then, dispatch it after subscribing the store.

store.subscribe(() => { console.log(store.getState()) })
store.dispatch(fetchData())

Now, the complete code goes like below.

const redux = require('redux')
const createStore = redux.createStore
const applyMiddleware = redux.applyMiddleware
const thunkMiddleware = require('redux-thunk').default
const axios = require('axios')
const initialState = {
loading: false,
data: [],
error: ''
}
const FETCH_DATA_REQUEST = 'FETCH_DATA_REQUEST'
const FETCH_DATA_SUCCESS = 'FETCH_DATA_SUCCESS'
const FETCH_DATA_FAILURE = 'FETCH_DATA_FAILURE'
const fetchDataRequest = () => {
return {
type: FETCH_DATA_REQUEST
}
}
const fetchDataSuccess = data => {
return {
type: FETCH_DATA_SUCCESS,
payload: data
}
}
const fetchDataError = error => {
return {
type: FETCH_DATA_FAILURE,
payload: error
}
}
const reducer = (state = initialState, action) => {
switch (action.type) {
case FETCH_DATA_REQUEST:
return {
...state,
loading: true
}
case FETCH_DATA_SUCCESS:
return {
loading: false,
data: action.payload,
error: ''
}
case FETCH_DATA_FAILURE:
return {
loading: false,
users: [],
error: action.payload
}
}
}
const fetchData = () => {
return function (dispatch) {
dispatch(fetchDataRequest())
axios.get("https://jsonplaceholder.typicode.com/users")
.then(response => {
const data = response.data.map(user => user.name)
dispatch(fetchDataSuccess(data))
})
.catch(error => {
dispatch(fetchDataError(error.message))
})
}
}
const store = createStore(reducer, applyMiddleware(thunkMiddleware))
store.subscribe(() => { console.log(store.getState()) })
store.dispatch(fetchData())

The output will display as below.

Now, modify the URL as incorrect.

const fetchData = () => {
return function (dispatch) {
dispatch(fetchDataRequest())
axios.get("https://jsossnplaceholder.typicode.com/users")
.then(response => {
const data = response.data.map(user => user.name)
dispatch(fetchDataSuccess(data))
})
.catch(error => {
dispatch(fetchDataError(error.message))
})
}
}

The output will now be displayed as below.

Summary

In this article, we have learned the concept of Middleware and how it is implemented in the Redux application. We have also learned about Async action, why it is required, and how it can be implemented in Redux. You can download the attached source code along with this article.

With this article, I've finished the concept of Redux. Now, I will move on to the learning of Redux in ReactJS. If you have any confusion or suggestions, please do comment.