React Redux

Redux Flow

Initial Steps for Redux

You need 9 steps to create a redux app

* Create Action
* Create Reducer
* Create Root reducer
* Configure Store
* Instantiate Store
* Connect Application to redux store
* Connect Component to redux
* Pass props via connect
* Dispatch action

Create Action

Pretty simple create function which returns an action. Don't forget to export

export function createCourse(course) {
   return {type: "CREATE_COURSE", course} 
}

Create Reducer

Simple Example

Note the reducer takes a state and an action. In this case state is an array. Also note the return is a new copy of state with the passed in course appended.

export default function courseReducer(state = [], action) {
  switch (action.type) {
    case "CREATE_COURSE":
      return [...state, { ...action.course }];
    default:
      return state;
  }
}

Rules

Reducer must not

• Mutate arguments
• Perform side effects
• Call non-pure functions

Pure Functions

Reducers must use pure functions where the outcome is always predictable. i.e. you cannot call mutable function. e.g.

 function multiply(a, b)
 {
   return a * b;
 }

• No side effects
• Also yields same result

Immutability

Way to be immutable

ES6 allows us to copy objects using Object.assign e.g.

var state = {color:'red', name: 'Adam', point:5}
var state2 = Object.assign({}, state, {point:50})

You can use map or filter, reduce, concat or spread as these all create a new object

Tools to enforce immutability

• Using trust with your team - relies on good code reviews
• Use redux-immutable-state-invarient a package to detect problems (not for prod)
• Enforce by using products like Immer, Immutable.js etc

Create root Reducer

This is used to combine reducers. In this example there is only one but there will be more.

import { combineReducers } from "redux";
import courses from "./courseReducer";

const rootReducer = combineReducers({
  courses,
});

export default rootReducer;

Configure Store

Simple Store

The simplest way to do this is

import { createStore } from "redux";
import rootDeducer from "./reducers";

export default function configureStore(initialState) {
  return createStore(rootDeducer, initialState);
}

Store with redux devtools

However here is a useful alternative which allows the use of redux devtools

import { createStore, applyMiddleware, compose } from "redux";
import rootDeducer from "./reducers";
import reduxImmutableStateInvariant from "redux-immutable-state-invariant";
export default function configureStore(initialState) {
  const composeEnhancers =
    window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;

  return createStore(
    rootDeducer,
    initialState,
    composeEnhancers(applyMiddleware(reduxImmutableStateInvariant()))
  );
}

Store with logging

This will show action prev state and next state

import {applyMiddleware,createStore } from 'redux';
import logger from 'redux-logger';

var store = createStore(
    amount,
    applyMidddleware(logger)
);

Combining Middleware

Note the middleware can be combined by comma separated values.

createStore(
    rootDeducer,
    initialState,
    composeEnhancers(applyMiddleware(reduxImmutableStateInvariant(), logger))

Connect Application to redux store

Create a redux store and pass it via a provider by surrounding the App with the redux provider

import React from "react";
import { render } from "react-dom";

import {Provider} from "react-redux"
import configureStore from "./redux/createStore"

const store = configureStore();

render(
    <Provider store={store}>
        <App />
    </Provider>
  document.getElementById("app")
);

Connect Component to redux

To connect a component to redux you need to call the connect function which takes two functions mapStateToProps and optionally mapDispatchToProps and pass your page as an argument

export default connect(mapStateToProps, mapDispatchToProps)(CoursesPage)

mapStateToProps

This is when you pass a mapping of your state to your properties and your own props which might not be in state.

function mapStateToProps(state, ownProps) {
    return {
     courses: state.courses
    }
}

mapDispatchToProps

Null argument

export default connect(mapStateToProps)(CoursePages)

// Usage
this.props.dispatch(courseActions.createCourses(this.state.course))

Wrap dispatch

Manually wrap each create with dispatch

function mapDispatchToProps(dispatch) {
    return {
        createCourse: course => dispatch(courseActions.createCourse(course))
    }
} 

// In the component
this.props.createCourse(course)

Using bindActionsCreator

import {bindActionCreators} from "redux"
...
function mapDispatchToProps(dispatch ) {
   return {
       actions: bindActionCreators(courseActions, dispatch)
   }
}

// usage
this.props.actions.createCourse(this.state.course)

Using object

change the mapDispatchToProps as an object

const mapDispatchToProps = {
  createCourse: courseActions.createCourse,
};

// usage
this.props.createCourse(this.state.course);

Add Feature

So once initial setup is completion going forward some steps are repeated for each feature

* Create Action
* Enhance Reducer
* Connect component
* Dispatch action

Setting types using keyMirror

Just a nice little tip. keyMirror stops you having to type more for const e.g.

export var ActionType = {
    const THIS_IS_A_CONST = "THIS_IS_A_CONST";
};

becomes

export var ActionType = keyMirror ({
    THIS_IS_A_CONST = null
});

Setting Initial State

People found it useful to have a initialState.js to allow people to see the shape of the store for all reducers.

export default {
  authors: [],
  courses: [],
};

Example on Git hub

You can find an example at [[1]]

Legacy Redux

Note ... is new syntax for spread

Stores often are stored in stores/configurationStore.js at the same level as compontents

import {createStore} from 'redux'

var defaultState = {
    originalAmount: 0.00
};

function amount(state = defaultState, action) {
    if(action == = 'CHANGE_ORIGIN_AMOUNT') {
        return {
            ...state,
            originalAmount: action.data
        }
        // return Object.assign({},state, {originalAmout: action.data})
    }
}

var store = createStore();

store.subscribe(function() {
    console.log('state', store.getState());
})

store.dispatch({type:'CHANGE_ORIGIN_AMOUNT', data: 30.00});
store.dispatch({type:'', data: 30.00});
store.dispatch({type:'', data: 30.00});

Legacy Redux with subscribing

Show us subscribing to the store to make sure updates passed down to the components.

class MainConponent extends React.Component {

    componentDidMount() {
        store.subscribe( () => {
            this.setState({});
        } )
    }

    render() {
        return (
           <div>
               <Conversion originalAmount={store.getState().originalAmount} />
           </div>        )
    }
}