# Redux Tutorial For Beginners

KrunalLathiya
72.2K views

## Redux Tutorial For Beginners

Redux is quite an excellent State Managment Framework usually used with React.js library. In Single Page Application, data management at client side is far more complicated than just imagine. Now, you are familiar that, ReactJS is relying on the State of the application. However, In React.js state management is possible, but when the application gets bigger and bigger, unwanted errors and data changes are detected, and which module has changed which state and which view is updated, all these matters get complex, and we feel like, we trapped in our application. Facebook gives the solution. Its developer has created one State management pattern called Flux.

## Flux

It complements React’s composable view components by utilizing the unidirectional data flow. When the users interact with views, the views propagates actions through a central dispatcher, to the various stores that hold the application data and logic, which updates all of our views that are affected.

Flux has so many stores, and each store is using different small part of the state or data of our application. In other words, each different module has its store.

## Flux Data Flow

1. The user interacts with the view and view triggers an action.
2. Action dispatch the corresponding function and then that function change the store.
3. When store updates its data, the subscriber views are automatically updated. We do not need to modify the data in different modules manually.

It is a unidirectional data flow. When the application gets bigger and bigger, then multiple stores manage the data.

When multiple stores are there, the condition of our application looks like above figure, but the data flow is Unidirectional.

Flux has Multiple Stores.

## Redux

Redux is the predictable state container for JavaScript applications. Redux is also following the Unidirectional flow, but it is entirely different from Flux. Flux has multiple stores.

Redux has a Single Store.

Redux can not have multiple stores. The store is divided into various state objects. So all we need is to maintain the single store, or we can say the only source of truth.

## Three Principles Of Redux

1. Single source of truth.
3. Changes are made with pure functions.

It is the state of our whole application is stored in an object within a single store. There is an only way to change the state is to emit an action, an object describing what happened. To specify how actions transform the state, you write pure reducers.

## Actions

Actions are payloads of information that send data from your application to your store. You send them to the store using store.dispatch()

Actions are plain JavaScript objects. Actions must have a type property that indicates the type of action being performed. Types should typically be defined as string constants.

import { ADD_TODO, REMOVE_TODO } from '../actionTypes'


## Action Creators

Action creators are exactly the functions that create actions.

function addTodo(text) {
return {
text
}
}


## Reducers

Actions describe the fact that something happened but don’t specify how the application’s state changes in response. That is the job of reducers.

## Handling Actions

This is called a reducer because it is the type of function you would pass to Array.prototype.reduce(reducer, ?initialValue). It is essential that the reducer stay pure.

Following are the things you should never do inside a reducer:

1. Mutate reducer’s arguments;
2. Perform side effects like database calls, API calls, and routing transitions;
3. Call non-pure functions, e.g., Date.now() or Math.random()

## Store

A store is an object that brings them together. A store has the following responsibilities:

1. Holds application state;
3. Allows state to be updated via dispatch(action);
4. Registers listeners via subscribe(listener);
5. It handles unregistering of listeners via the function returned by subscribe(listener)

t is important to note that you will only have a single store in a Redux application. If you want to split your data handling logic, you will use reducer composition instead of many stores.

import { createStore } from 'redux'
import todoApp from './reducers'
let store = createStore(todoApp)


## Redux Tutorial With Example

Create one project folder and in that create one file called package.json. Copy the following code into it.

{
"name": "reduxapp",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"start": "webpack-dev-server"
},
"author": "KRUNAL LATHIYA",
"devDependencies": {
"babel-core": "^6.24.0",
"babel-preset-es2015": "^6.24.0",
"babel-preset-react": "^6.23.0",
"babel-preset-stage-3": "^6.22.0",
"webpack": "^2.3.2",
"webpack-dev-server": "^2.4.2"
},
"dependencies": {
"react": "^15.4.2",
"react-dom": "^15.4.2",
"react-redux": "^5.0.6",
"redux": "^3.7.2"
}
}


Switch to a terminal and type the following command.

npm install


Next step will be to create the webpack.config.js file in the root folder.

// webpack.config.js

module.exports = {
entry: './src/main.js',
output: {
filename: 'bundle.js'
},
module: {
{
test: /\.js\$/,
exclude: /node_modules/
}
]
},
devServer: {
port: 3000
}
};


Also, create one file called in root called .babelrc

{
"presets": ["es2015", "react", "stage-3"]
}


Make one file in the root called index.html

<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>Redux Tutorial 2017</title>
<body>
<div id="root"></div>
</body>
</html>


Go to a terminal and type this command.

npm start


Server will start at this URL: http://localhost:3000

// main.js

import React from 'react';
import { render } from 'react-dom';
import { Provider } from 'react-redux';
import App from './components/App';

render(
<Provider>
<App />
</Provider>,
document.getElementById('root')
)


I have included the react particular dependency, but also I have included react-redux. It provides us a store through our entire application. So our App element is wrapped around Provider.

## Step 3: Create components directory inside src.

Make one directory and inside make our most important component file called App.js

// App.js

import React from 'react';

const App = () => {

<div className="container">
App Component
</div>

}
export default App;


App.js the component where our other components are included. We are creating the simple counter application. However, we need to define first how many components are required to complete the application.

There are mainly two types of components when you are dealing with React and Redux.

1. Smart Component
2. Dumb Component

## Smart Component

The smart component is the kind of component, which directly interacts with the state of our application. It has access to the store and it can either dispatch the actions or get the current state of our application. It is the smart components because when the store is changed, by default, it subscribes the new state and changes the view according to it. In our application, there are three smart components.

1. Counter.js
3. RemoveCounter.js

All these smart components are put in the containers folder, which I will create later in this article. Container components only contain that components that are smart.

## Dumb Component

App.js is the Dumb component, it includes the child component but, it does not interact the store. So we put that component inside components folder.

## Step 4: Create container dir. Inside src folder.

We need to create three container components inside this directory as I have mentioned before. We are creating AddCounter.js component.

// AddComponent.js

import React, { Component } from 'react';
import { connect } from 'react-redux';
import { addCounter } from '../actions';
import { bindActionCreators } from 'redux';

constructor(props) {
super(props);
}
render() {
return (
<div className="container">
<form>
<div className="field is-grouped">
<div className="control">
<button className="button is-primary"
</button>
</div>
</div>
</form>
</div>
)
}
}
function mapDispatchToProps(dispatch) {
return { actions: bindActionCreators(addCounter, dispatch) }
}


Here, I need to explain lots of things so let us get started.

If AddCounter component is container component, then it connects to the store remember, that is why it is a smart component.

So the last line of the code is that we are connecting our component to the Redux store.

When the user clicks the button according to Redux principle, it dispatches an action, so we need to pass dispatch function as a property to this component.

Now, it dispatches the action, and in our scenario, it named as addCounter(). So addCounter return an action.

## Create an Action

Make one folder inside src called actions and in that create one file called index.js

// index.js

import * as actionType from './ActionType';

export const addCounter = () => ({
});


So as I mentioned, It returns an object describes our actions.

Here, I have also included one more file called ActionType.js

This file is needed because all the action names are constant and if we create one file, which only exports the naming constant then it is easy for us to define any action without any typos because actions names are on the strings.

## Make ActionType.js

This file is inside actions directory.

// ActionType.js

export const REMOVE_COUNTER = 'REMOVE_COUNTER';


Now, coming to the point, we are at AddCounter.js file, right?

// AddCounter.js

import React, { Component } from 'react';
import { connect } from 'react-redux';
import { addCounter } from '../actions';
import { bindActionCreators } from 'redux';

constructor(props) {
super(props);
}
render() {
return (
<div className="container">
<form>
<div className="field is-grouped">
<div className="control">
<button className="button is-primary"
</button>
</div>
</div>
</form>
</div>
)
}
}
function mapDispatchToProps(dispatch) {
return { actions: bindActionCreators(addCounter, dispatch) }
}


Function mapDispatchToProps is needed because we need to pass dispatch as a property to our component and also we need to bind the actions with this component.

## Step 5: Create reducer directory inside src and make one file

Make one file called counterReducer.js inside reducer directory.

// counterReducer.js

import * as actionType from '../actions/ActionType';

const counterReducer = (state = 0, action) => {
let newState;
switch (action.type) {
return newState = state + action.payload;
case actionType.REMOVE_COUNTER:
return newState = state - action.payload;
default:
return state
}
}

export default counterReducer;


Please note that I have described both cases in here

1. Increment (for add +1 in counter state)
2. Decrement (decrease one from counter state)

If you carefully see the above cases then, I have not modified the state directly. See, I have defined a new variable and then assign new state in that variable and return that variable.

So, it is a pure function, which is not mutating any store state, just take the old state value and add that old value plus new value and assign it to the variable and return the new state of our application. This is the central principle of Redux after all.

Make one file inside reducer directory called index.js

// index.js

import { combineReducers } from 'redux';
import counterReducer from './counterReducer';

const counterApp = combineReducers({
counterReducer
})

export default counterApp


Now, this is our single and final store. This is the store we include in our main.js file. combineReducer() function as the name suggests to combine all reducers in one store and return as a global application state object.

Now, our main.js file will look like this. I have passed the store to our entire application. Also Included the reducers.

// main.js

import React from 'react';
import { render } from 'react-dom';
import { createStore } from 'redux';
import { Provider } from 'react-redux';
import App from './components/App';
import reducer from './reducers';

const store = createStore(reducer);

render(
<Provider store={store}>
<App />
</Provider>,
document.getElementById('root')
)


## Step 6: Create same smart component for RemoveCounter.js

Make RemoveCounter.js inside container directory.

// RemoveCounter.js

import React, { Component } from 'react';
import { connect } from 'react-redux';
import { removeCounter } from '../actions';
import { bindActionCreators } from 'redux';

class RemoveCounter extends Component {
constructor(props) {
super(props);
}
render() {
return (
<div className="container">
<form>
<div className="field is-grouped">
<div className="control">
<button className="button is-primary"
onClick={(e) => {e.preventDefault();this.props.dispatch(removeCounter())}}>
Remove
</button>
</div>
</div>
</form>
</div>
)
}
}
function mapDispatchToProps(dispatch) {
return { actions: bindActionCreators(removeCounter, dispatch) }
}

export default connect(mapDispatchToProps)(RemoveCounter);


Now, switch to src >> actions >> index.js and add new action for removeCounter. So our final file looks like this.

// index.js

import * as actionType from './ActionType';

export const addCounter = () => ({
});

export const removeCounter = () => ({
type: actionType.REMOVE_COUNTER,
});


We have already defined the decrement reducer.

// counterReducer.js

import * as actionType from '../actions/ActionType';

const counterReducer = (state = 0, action) => {
let newState;
switch (action.type) {
return newState = state + action.payload;
case actionType.REMOVE_COUNTER:
return newState = state - action.payload;
default:
return state
}
}

export default counterReducer;


## Step 7: Now final smart component remains is Counter.js

// Counter.js

import React, { Component } from 'react';
import { connect } from 'react-redux';

class Counter extends Component {
constructor(props){
super(props);
}
render(){
return (
<div className="cotainer">
<h1>
{this.props.count}
</h1>
</div>
</div>
)
}
}
function mapStateToProps(state){
return {
count: state.counterReducer,
};
}
export default connect(mapStateToProps)(Counter);


This is the smart component, so we need to connect it with Redux store. So we have connected it with the store and fetched the latest state from the store and display it.

mapStateToProps maps the state to the props of current component and shows the data as a property of the component.

## Step 8: Include all the components into the App.js file.

// App.js

import React from 'react';
import Counter from '../containers/Counter';
import RemoveCounter from '../containers/RemoveCounter';

const App = () => {
return (
<div className="container">
<Counter></Counter><br />
<div className="columns">
<div className="column is-11">
</div>
<div className="column auto">
<RemoveCounter></RemoveCounter>
</div>
</div>
</div>
)
}
export default App;

npm start


If you switch to this URL: http://localhost:3000. You can see a counter application.

Redux Tutorial For Beginners