Develop Reference

Implementing Higher-Order Components in React - Redux

I am building an app with react / redux for managing Collection of Electronic equipment (=donations). I have several routes that their functionality - is similiar - fetching entity (it could be volunteer, donor etc) data and show it in a table.
the volunteer route:
import React, {Component} from 'react';
import { connect } from 'react-redux';
import { requestVolunteerData } from '../actions/entitiesAction';
import { volenteerColumns as columns } from '../utils/entitiesColumns/volenteerColumns';
import '../container/App.css';
import Table from '../components/Table/Table';
import Loading from '../components/Loading/Loading';
const mapStateToProps = state => {
return {
entities: state.requestEntitiesReducer.entities,
isPending: state.requestEntitiesReducer.isPending,
error: state.requestEntitiesReducer.error
}
}
const mapDispatchToProps = dispatch => {
return {
onRequestEntities: () => dispatch(requestVolunteerData())
}
}
class Volenteer extends Component{
componentDidMount () {
this.props.onRequestEntities();
}
render () {
const { entities, isPending} = this.props;
return isPending ?
<Loading />
:
(
<div className='tc'>
<h1 className='f2'>רשימת מתנדבים</h1>
<Table data={ entities } columns={ columns } />
</div>
);
}
}
export default connect(mapStateToProps, mapDispatchToProps)(Volenteer);
and a consumer route look like this:
import React, {Component} from 'react';
import { connect } from 'react-redux';
import { requestConsumerData } from '../actions/entitiesAction';
import { consumerColumns as columns } from '../utils/entitiesColumns/consumerColumns';
import '../container/App.css';
import Table from '../components/Table/Table';
import Loading from '../components/Loading/Loading';
const mapStateToProps = state => {
return {
entities: state.requestEntitiesReducer.entities,
isPending: state.requestEntitiesReducer.isPending,
error: state.requestEntitiesReducer.error
}
}
const mapDispatchToProps = dispatch => {
return {
onRequestEntities: () => dispatch(requestConsumerData())
}
}
class Consumer extends Component{
componentDidMount () {
this.props.onRequestEntities();
}
render () {
const { entities, isPending} = this.props;
return isPending ?
<Loading />
:
(
<div className='tc'>
<h1 className='f2'>רשימת נזקקים</h1>
<Table data={ entities } columns={ columns }/>
</div>
);
}
}
export default connect(mapStateToProps, mapDispatchToProps)(Consumer);
As you can see, they both have the same logic and the differences are:
the action
the Entity name for the h1 tag
the columns object
the data of course
so I tried to implement an HOC which look like this:
import React, {Component} from 'react';
import { connect } from 'react-redux';
import '../container/App.css';
import Table from '../Table/Table';
import Loading from '../Loading/Loading';
export default function WithEntity (EntityComponent, action, columns, name) {
const mapStateToProps = state => {
return {
isPending: state.requestEntitiesReducer.isPending,
entities: state.requestEntitiesReducer.entities,
error: state.requestEntitiesReducer.error
}
}
const mapDispatchToProps = dispatch => {
return {
onRequestEntities: () => dispatch(action)
}
}
class extends Component {
componentDidMount () {
this.props.onRequestEntities();
}
render() {
return (
<EntityComponent {...this.props} />
)
}
}
return connect(mapStateToProps, mapDispatchToProps)(EntityComponent);
}
and the volunteer should look like:
const volunteerHoc = WithEntity (volunteer, action, columns, name);
const consumerHoc = WithEntity (consumer, action, columns, name)
but I did not understand how to inject the Loading and Table components, and wht the name of the class inside the HOC should be-
should I use another HOC - something like WithLoader that receive the data from the first one and render the Loading and Table components with the proper data? just to mention that connect is HOC itself so I need to return the EntityComponent to the redux store :
return connect(mapStateToProps, mapDispatchToProps)(EntityComponent);
I Would appreciate any help

OK, I made it, the HOC takes a basic component, Expands the functionality (by adding methods and managing state for ex) and return a new (henanced) comp with this props.
lets create a simple volunteer comp:
import React, {Component} from 'react';
import { requestVolunteerData } from '../actions/entitiesAction';
import { volenteerColumns as columns } from '../utils/entitiesColumns/volenteerColumns';
import '../container/App.css';
import WithEntity from '../components/HOC/WithEntity.jsx';
import Table from '../components/Table/Table';
import Loading from '../components/Loading/Loading';
class Volenteer extends Component {
render() {
const { entities, isPending} = this.props;
return isPending ?
<Loading />
:
(
<div className='tc'>
<h1 className='f2'>רשימת מתנדבים</h1>
<Table data={ entities } columns={ columns } />
</div>
);
}
}
const VolenteerHOC = WithEntity(Volenteer, requestVolunteerData() );
export default VolenteerHOC;
now lets create the HOC WithEntity that managing the state and return the new cmop to redux state by connect:
import React, {Component} from 'react';
import { connect } from 'react-redux';
const WithEntity = (EntityComponent, action) => {
const mapStateToProps = state => {
return {
isPending: state.requestEntitiesReducer.isPending,
entities: state.requestEntitiesReducer.entities,
error: state.requestEntitiesReducer.error
}
}
const mapDispatchToProps = dispatch => {
return {
onRequestEntities: () => dispatch(action)
}
}
class NewCmoponent extends Component {
componentDidMount () {
this.props.onRequestEntities();
}
render() {
const { entities, isPending} = this.props;
return (
<EntityComponent {...this.props} />
)
}
}
return connect(mapStateToProps, mapDispatchToProps)(NewCmoponent );
}
export default WithEntity;
Now same route can be simply generated via this HOC.
check out this video:
https://www.youtube.com/watch?v=rsBQj6X7UK8

React Mobx can't display observable contents, very simple app

Very simple app, I'm trying to display content from my API using Mobx and Axios, here's my Axios agent.ts:
import { ITutorialUnit } from './../model/unit';
import axios, { AxiosResponse } from "axios";
//set the base URL
axios.defaults.baseURL = "http://localhost:5000/api";
//store our request in a const
const responseBody = (response: AxiosResponse) => response.data;
const requests = {
get: (url: string) => axios.get(url).then(responseBody),
};
//create a const for our activty's feature,all our activities' request are go inside our Activities object
const TutorialUnits = {
list: ():Promise<ITutorialUnit[]> => requests.get("/tutorialunits"),
};
export default{
TutorialUnits
}
then I call this agent.s in a store:
import { ITutorialUnit } from "./../model/unit";
import { action, observable } from "mobx";
import { createContext } from "react";
import agent from "../api/agent";
class UnitStore {
#observable units: ITutorialUnit[] = [];
//observable for loading indicator
#observable loadingInitial = false;
#action loadUnits = async () => {
//start the loading indicator
this.loadingInitial = true;
try {
//we use await to block anything block anything below list() method
const units = await agent.TutorialUnits.list();
units.forEach((unit) => {
this.units.push(unit);
// console.log(units);
});
this.loadingInitial = false;
} catch (error) {
console.log(error);
this.loadingInitial = false;
}
};
}
export default createContext(new UnitStore());
then I call this in my App component:
import React, { Fragment, useContext, useEffect } from "react";
import { Container } from "semantic-ui-react";
import "semantic-ui-css/semantic.min.css";
import NavBar from "../../features/nav/NavBar";
import { ActivityDashboard } from "../../features/Units/dashboard/tutorialUnitDashboard";
import UnitStore from "../stores/unitStore";
import { observer } from "mobx-react-lite";
import { LoadingComponent } from "./LoadingComponent";
const App = () => {
const unitStore = useContext(UnitStore);
useEffect(() => {
unitStore.loadUnits();
//need to specify the dependencies in dependenciy array below
}, [unitStore]);
//we are also observing loading initial below
if (unitStore.loadingInitial) {
return <LoadingComponent content="Loading contents..." />;
}
return (
<Fragment>
<NavBar />
<Container style={{ marginTop: "7em" }}>
<ActivityDashboard />
</Container>
</Fragment>
);
};
export default observer(App);
Finally, I want to use this component to display my content:
import { observer } from "mobx-react-lite";
import React, { Fragment, useContext } from "react";
import { Button, Item, Label, Segment } from "semantic-ui-react";
import UnitStore from "../../../app/stores/unitStore";
const UnitList: React.FC = () => {
const unitStore = useContext(UnitStore);
const { units } = unitStore;
console.log(units)
return (
<Fragment>
{units.map((unit) => (
<h2>{unit.content}</h2>
))}
</Fragment>
);
};
export default observer(UnitList);
I can't see the units..
Where's the problem? My API is working, I tested with Postman.
Thanks!!

If you were using MobX 6 then you now need to use makeObservable method inside constructor to achieve same functionality with decorators as before:
class UnitStore {
#observable units: ITutorialUnit[] = [];
#observable loadingInitial = false;
constructor() {
// Just call it here
makeObservable(this);
}
// other code
}
Although there is new thing that will probably allow you to drop decorators altogether, makeAutoObservable:
class UnitStore {
// Don't need decorators now anywhere
units: ITutorialUnit[] = [];
loadingInitial = false;
constructor() {
// Just call it here
makeAutoObservable(this);
}
// other code
}
More info here: https://mobx.js.org/react-integration.html

the problem seems to be the version, I downgraded my Mobx to 5.10.1 and my mobx-react-lite to 1.4.1 then Boom everything's fine now.

.map dont show list (from API)

thanks in advance!!
I'm in trouble, I dont know whats wrong with my map hehe. I'm a new student (JS, React, Redux). It'd should show a list (or at least one name, anything), but nothing happen.
import React, {Component} from "react";
import { connect } from "react-redux";
import { push } from "connected-react-router";
import { getTrips } from "../../actions/allActions";
import List from "#material-ui/core/List";
class ListTrips extends Component {
componentDidMount() {
this.props.getTripsAction();
}
render() {
return (
<List>
{
this.props.trips.map((trip) => {
return(<li>{trip.name}</li>)
})
}
</List>
);
}
}
const mapStateToProps = state => ({
trips: state.trips.trips
});
const mapDispatchToProps = dispatch => ({
getTripsAction: () => dispatch(getTrips()),
});
export default connect(
mapStateToProps,
mapDispatchToProps
)(ListTrips)

New Components in Application cannot connect to redux

I have created a small application and connected it to Redux. Unfortunately when creating new components and using the same exact code those new components cannot seem to connect to redux and get undefined when accessing it (using mapStateToProps).
I have tried to create new Components and connect them again to no avail. I'm kind of at loss as to why it isn't working especially since the rest of the application can connect and get the state properly
index.js:
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import { Provider } from 'react-redux'
import store from './store'
ReactDOM.render(
<Provider store={store} >
<App />
</Provider>
, document.getElementById('root'));
store.js:
const initialState = {
guessedTimezone: '',
timezone: '',
pseudo: '',
};
function rootReducer(state = initialState, action) {
console.log(action);
if (action.type === 'CHANGE_TIMEZONE') {
return Object.assign({}, state, {
timezone: action.timezone,
guessedTimezone: action.guessedTimezone
})
}
if (action.type === 'CHANGE_PSEUDO') {
return Object.assign({}, state, {
pseudo: action.pseudo,
token: action.token
})
}
return state;
}
export default rootReducer;
new Component not connecting:
import React, { Component } from 'react'
import { connect } from 'react-redux'
export class TestPseudo extends Component {
render() {
console.log(this.props.pseudo);
return (
<div>
{this.props.pseudo}
</div>
)
}
}
const mapStateToProps = state => {
return {
pseudo: state.pseudo
}
}
export default connect(mapStateToProps)(TestPseudo)
Here for example this.props.pseudo returns undefined when, if the connection happens, it should return the value if i understand it correctly and yet it shows undefined
EDIT:
App.js as per requested :
import React, { Component } from 'react'
import { connect } from 'react-redux'
import Homepage from './Components/Homepage';
import moment from 'moment';
import moment_timezone from 'moment-timezone';
import HeaderApp from './Components/HeaderApp';
import { TestPseudo } from './Components/TestPseudo';
export class App extends Component {
async componentDidMount() {
let tz = moment.tz.guess(true);
let date = moment(new Date()).local();
let timezone = date['_i'].toString().split('(')[1].split(')')[0];
this.props.dispatch({
type: 'CHANGE_TIMEZONE',
guessedTimezone: tz,
timezone: timezone
})
console.log(`Guessed timezone: ${tz} (${timezone})`);
}
_showHomepage() {
if (this.props.showHomepage && this.props.loaded) {
return (
<div style={styles.mainWindow}>
{/*<Homepage click={this._handleClick} />*/}
<TestPseudo />
</div>
)
}
}
_showHeader() {
return (
<div>
<HeaderApp />
</div>
)
}
render() {
return (
<div>
{this._showHeader()}
{this._showHomepage()}
</div>
)
}
}
const styles = {
mainWindow: {
height: '100vh',
width: '100vw'
}
}
const mapStateToProps = state => {
return {
guessedTimezone: state.guessedTimezone,
timezone: state.timezone,
};
};
export default connect(mapStateToProps)(App);
I call that new Component instead of my old Component. The homepage can connect but not the new one so i think it's not a problem of emplacement

I think its here
import { TestPseudo } from './Components/TestPseudo';
You are importing the non-connected component. Try this
import TestPseudo from './Components/TestPseudo';
For your understanding, exporting as default can be imported like so;
export default Component
import WhateverName from ....
Named export like const or in your case class;
export class Component
import { Component } from ...
So use brackets when Named, and skip brackets when default.

higher order component can't see props

I'm using react with react-native and redux. The error comes to the component from the redux store. After that, i received: Nothing was returned from render. This usually means a return statement is missing. Or, to render nothing, return null.
What is wrong with this? why hoc can't see the props?
My component:
import React, { Component } from 'react';
import withHandleError from './withHandleError';
class SendScreen extends Component {
render() {
const { error } = this.props;
return (
<div> Test </div>
)
}
};
const mapStateToProps = ({ppm}) => ({
error: ppm.error
})
export default withHandleError(connect(mapStateToProps)(SendScreen));
And HoC:
import React, { Component } from 'react';
import { ErrorScreen } from '../../ErrorScreen';
import { View } from 'react-native';
export default Cmp => {
return class extends Component {
render() {
const {error, ...rest } = this.props;
console.log(error) //// undefined....
if (error) {
return <ErrorScreen />
}
return <Cmp { ...rest } />
}
}
}

The order is which you call the HOCs matters when you want to access props supplied by one in another. Re-ordering your connect and withHandleError HOC will work
import React, { Component } from 'react';
import withHandleError from './withHandleError';
class SendScreen extends Component {
render() {
const { error } = this.props;
return (
<div> Test </div>
)
}
};
const mapStateToProps = ({ppm}) => ({
error: ppm.error
})
export default connect(mapStateToProps)(withHandleError(SendScreen));