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RxJS in Action Ch10 5B: Building the application
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// file: src/index.js - Derived from: | |
// RxJS in Action (2017, Manning), 978-1-617-29341-2 | |
// by Paul P. Daniels and Luis Atencio | |
// Listings: | |
// 10.6 Plugging into the middleware (p.297) | |
// 10.7 Implementing custom ofType operator (p.299) | |
// 10.8 Building your middleware (p.299) | |
// 10.9 Building the application (p.302) | |
// | |
// Variation B: | |
// - getState from exposed value of BahaviorSubject | |
// - Use React's Context and introduce WithdrawConnect component | |
import React, {Component} from 'react'; | |
import PropTypes from 'prop-types'; | |
import ReactDOM from 'react-dom'; | |
import registerServiceWorker from './registerServiceWorker'; | |
import { createStore } from 'redux'; | |
import Rx from 'rxjs'; | |
import PouchDB from 'pouchdb-browser'; | |
// --- Listing 10.7 Implementing custom ofType operator | |
// ** Use filterOnType in lieu of monkey patching | |
// ** Rx.Observable.prototype.ofType | |
const ofType = (types) => { | |
switch (types.length) { | |
case 0: | |
throw new Error('Must specify at least one type!'); | |
case 1: | |
return ({type}) => type === types[0]; | |
default: | |
return ({type}) => types.indexOf(type) > -1; | |
} | |
}; | |
const filterOnType = (action$, ...types) => | |
action$.filter(ofType(types)); | |
// --- Listing 10.7 end | |
const CHECKING = 'checking'; | |
const SAVINGS = 'savings'; | |
const getBalance = (account, state) => state[account]; | |
// action type | |
const TX_LOG = 'TX_LOG'; | |
const LOG = 'LOG'; | |
const WITHDRAW = 'WITHDRAW'; | |
const DEPOSIT = 'DEPOSIT'; | |
// action creators | |
const withdraw = (payload) => ({ | |
type: TX_LOG, | |
payload: {...payload, type: WITHDRAW} | |
}); | |
const deposit = (payload) => ({ | |
type: TX_LOG, | |
payload: {...payload, type: DEPOSIT} | |
}); | |
// | |
const depositAmount = (balance, amount) => balance + amount; | |
const withdrawAmount = (balance, amount) => balance - amount; | |
const updateBalance = (update, {account, amount}, state) => { | |
return typeof amount !== 'number' | isNaN(amount) || amount <= 0 ? | |
state : | |
{...state, [account]: update(getBalance(account, state), amount)}; | |
}; | |
// state updates | |
const depositTo = (payload, state) => | |
updateBalance(depositAmount, payload, state); | |
const withdrawFrom = (payload, state) => | |
updateBalance(withdrawAmount, payload, state); | |
// reducer | |
const updateAccounts = (state, action) => { | |
const {type, payload} = action; | |
switch(type) { | |
case WITHDRAW: | |
return withdrawFrom(payload, state); | |
case DEPOSIT: | |
return depositTo(payload, state); | |
case LOG: | |
console.log(payload.message); | |
return state; | |
default: | |
return state; | |
// eslint-disable-next-line no-unreachable | |
}; | |
}; | |
// --- Context | |
const StateContext = React.createContext(); | |
// --- Listing 10.6 (p.297) Plugging into the middleware | |
const txDb = new PouchDB('transactions'); | |
class Transaction { | |
constructor(type, account, amount, balance, timestamp) { | |
this.type = type; | |
this.account = account; | |
this.amount = amount; | |
this.balance = balance; | |
this.timestamp = timestamp; | |
} | |
} | |
const txWriteFailure = tx => | |
_err => Rx.Observable.of({type: LOG, payload: {message: 'TX WRITE FAILURE', tx}}); | |
const transactionLogEpic = (action$, store) => { | |
const attachBalance = obj => { | |
const {value: {payload: {account}}} = obj; | |
const balance = getBalance(account, store.getState()); | |
return {...obj, balance}; | |
}; | |
const splitActionTx = ({value: {payload: data}, balance, timestamp}) => { | |
const {type, ...payload} = data; | |
const {amount, account} = payload; | |
const tx = new Transaction(type, account, amount, balance, timestamp); | |
return [{type, payload}, tx]; | |
}; | |
const postTx = ([action, tx]) => { | |
let source$; | |
try { | |
const promise = txDb.post(tx); | |
source$ = Rx.Observable.fromPromise(promise); | |
} catch(error) { | |
source$ = Rx.Observable.throw(error); | |
} | |
return ( | |
source$ | |
.mapTo(action) | |
.catch(txWriteFailure(tx)) | |
); | |
}; | |
return ( | |
filterOnType(action$, TX_LOG) | |
.timestamp() | |
.map(attachBalance) | |
.map(splitActionTx) | |
.mergeMap(postTx) | |
); | |
}; | |
// --- Listing 10.6 end | |
// p.303 | |
const computeInterest = p => 0.1 / 365 * p; | |
const interestEpic = (action$, store) => { | |
const account = SAVINGS; | |
const getAccountBalance = () => getBalance(account, store.getState()); | |
const depositInterest = balance => deposit({account, amount: computeInterest(balance)}); | |
return ( | |
Rx.Observable | |
.interval(2000) | |
.map(getAccountBalance) | |
.map(depositInterest) | |
); | |
}; | |
// --- Listing 10.8 Building your middleware | |
const createMiddleware = (store, epics) => { | |
const source$ = new Rx.Subject(); | |
const dispatchToStore = action => store.dispatch(action); | |
const attachEpic = epic => epic(source$, store); | |
const attachedEpics = epics.map(attachEpic); | |
const combinedEpics$ = | |
Rx.Observable | |
.merge(...attachedEpics) | |
.publish(); | |
combinedEpics$.subscribe(source$); // Ouroboros | |
combinedEpics$.subscribe(dispatchToStore); | |
const dispatch = action => source$.next(action); | |
return [combinedEpics$, dispatch]; | |
}; | |
// --- Listing 10.8 end | |
// p.290 | |
const createStreamFromStore = (store) => { | |
const getState = () => store.getState(); | |
const initial = getState(); | |
const stateSubject$ = new Rx.BehaviorSubject(initial); | |
const state$ = | |
Rx.Observable | |
.from(store) | |
.map(getState) | |
.multicast(stateSubject$) | |
.refCount(); | |
return [state$, () => stateSubject$.value]; | |
}; | |
const appStatePropType = PropTypes.shape({ | |
state$: PropTypes.shape({ | |
subscribe : PropTypes.func.isRequired, | |
}).isRequired, | |
dispatch : PropTypes.func.isRequired, | |
getState : PropTypes.func.isRequired | |
}); | |
// Presentation Components | |
const locale = 'en-US'; | |
const currency = 'USD'; | |
const balanceFormat = | |
new Intl.NumberFormat(locale, {style: 'currency', currency}); | |
const AccountBalance = ({name, amount}) => | |
<div>{name}: {balanceFormat.format(amount)}</div>; | |
AccountBalance.propTypes = { | |
name : PropTypes.string, | |
amount : PropTypes.number | |
}; | |
const BalancesView =({checking, savings}) => | |
<div> | |
<AccountBalance {...{name: 'Checking', amount: checking}}/> | |
<AccountBalance {...{name: 'Savings', amount: savings}}/> | |
</div>; | |
BalancesView.propTypes = { | |
checking : PropTypes.number, | |
savings : PropTypes.number | |
}; | |
const toName = account => { | |
if(account && (typeof account === 'string') && (account.length > 0)){ | |
const name = account.trim(); | |
return name.charAt(0).toUpperCase() + name.slice(1).toLowerCase(); | |
} | |
return ''; | |
}; | |
const WithdrawView = ({amount, account, onChange, onClick}) => { | |
const type = 'number'; | |
const value = typeof amount === 'number' ? amount : ''; | |
return ( | |
<div> | |
<fieldset> | |
<legend>Withdraw amount from {toName(account)}:</legend> | |
<input {...{type, value, onChange}} /> | |
</fieldset> | |
<button {...{onClick}}>Withdraw</button> | |
</div> | |
); | |
}; | |
WithdrawView.propTypes = { | |
amount : PropTypes.number, | |
account : PropTypes.string.isRequired, | |
onChange : PropTypes.func.isRequired, | |
onClick : PropTypes.func.isRequired | |
}; | |
// Container Component | |
const initialAmount = () => ({amount: undefined}); | |
class WithdrawContainer extends Component { | |
constructor(props) { | |
super(props); | |
this.state = initialAmount(); | |
} | |
onChange = ({target: {value}}) => { | |
const newAmount = parseFloat(value); | |
const amount = | |
isNaN(newAmount) || newAmount < 0 ? | |
initialAmount().amount : | |
newAmount; | |
this.setState(prevState => ({...prevState, amount})); | |
} | |
handleClick = _event => { | |
const { | |
props: {withdraw, balance}, | |
state: {amount} | |
} = this; | |
if (typeof amount !== 'number') { | |
this.setState(initialAmount); | |
} else if (balance > amount) { | |
withdraw(amount); | |
} else { | |
throw new Error('Overdraft error!'); | |
} | |
} | |
render() { | |
const {handleClick: onClick, onChange, props: {account}, state: {amount}} = this; | |
return <WithdrawView {...{amount, account, onChange, onClick}} />; | |
} | |
} | |
WithdrawContainer.propTypes = { | |
account : PropTypes.string.isRequired, | |
balance : PropTypes.number.isRequired, | |
withdraw : PropTypes.func.isRequired | |
}; | |
// Connect Component | |
const mapStateToProps = (state, props) => ({balance: getBalance(props.account, state)}); | |
const mapDispatchToProps = (dispatch, props) => ({ | |
withdraw: (amount => dispatch(withdraw({amount, account: props.account}))) | |
}); | |
const mergeProps = (stateProps, dispatchProps, props) => | |
({...stateProps, ...dispatchProps, ...props}); | |
class WithdrawConnect extends Component { | |
constructor(props) { | |
super(props); | |
this.state = {balance: 0}; | |
this.subscription = null; | |
this.dispatchProps = null; | |
} | |
handleChange = (newState) => { | |
const {state: balance, props} = this; | |
const newProps = mapStateToProps(newState, props); | |
if (balance !== newProps.balance) { | |
this.setState((_prevState, _props) => newProps); | |
} | |
}; | |
subscribe = (state$, dispatch) => { | |
const {props} = this | |
if(!this.subscription){ | |
this.dispatchProps = mapDispatchToProps(dispatch, props); | |
this.subscription = state$.subscribe(this.handleChange); | |
} | |
}; | |
componentWillUnmount() { | |
const {subscription} = this; | |
if(subscription) { | |
subscription.unsubscribe(); | |
this.subscription = null; | |
this.dispatchProps = null; | |
} | |
} | |
withContext = ({state$, dispatch, getState}) => { | |
const {subscription, state, props} = this; | |
let stateProps; | |
if(subscription) { | |
stateProps = state; | |
} else { | |
this.subscribe(state$, dispatch); | |
stateProps = mapStateToProps(getState(), props); | |
} | |
const withdrawProps = mergeProps(stateProps, this.dispatchProps, props); | |
return <WithdrawContainer {...{...withdrawProps}} /> | |
}; | |
render() { | |
return <StateContext.Consumer>{this.withContext}</StateContext.Consumer>; | |
} | |
} | |
WithdrawConnect.propTypes = { | |
account : PropTypes.string.isRequired, | |
}; | |
// --- Listing 10.9 Building the application | |
class Balances extends Component { | |
constructor(props) { | |
super(props); | |
this.unsubscribe = null; | |
} | |
handleChange = (_state) => { | |
this.forceUpdate(); // Trigger render | |
} | |
componentDidMount() { | |
const {handleChange, props: {subscribe}} = this; | |
this.unsubscribe = subscribe(handleChange); | |
} | |
componentWillUnmount() { | |
const {unsubscribe} = this; | |
if(unsubscribe) { | |
unsubscribe(); | |
this.unsubscribe = null; | |
} | |
} | |
render() { | |
const {props: {appState}} = this; | |
const accounts = appState.getState(); | |
const account = CHECKING; | |
return ( | |
<StateContext.Provider {...{value: appState}}> | |
<BalancesView {...accounts} /> | |
<WithdrawConnect {...{account}}/> | |
</StateContext.Provider> | |
); | |
} | |
}; | |
Balances.propTypes = { | |
subscribe : PropTypes.func.isRequired, | |
appState : appStatePropType.isRequired | |
}; | |
// initial state | |
const accounts = () => ({ | |
[CHECKING]: 100, | |
[SAVINGS]: 100 | |
}); | |
const epics = [ // p.298 | |
transactionLogEpic, | |
interestEpic | |
]; | |
const store = createStore(updateAccounts, accounts()); | |
const [epics$, dispatch] = createMiddleware(store, epics); | |
const [state$, getState] = createStreamFromStore(store); | |
const appState = {state$, dispatch, getState}; | |
const subscribe = ((state$, epics$) => | |
(...args) => { | |
const stateSub = state$.subscribe(...args); | |
const epicsSub = epics$.connect(); | |
const unsubscribe = () => { | |
stateSub.unsubscribe(); | |
epicsSub.unsubscribe(); | |
}; | |
return unsubscribe; | |
} | |
)(state$, epics$); | |
ReactDOM.render( | |
<Balances {...{subscribe, appState}} />, | |
document.getElementById('root') | |
); | |
// --- Listing 10.9 end | |
registerServiceWorker(); | |
// cleanup | |
(() => { | |
const secs30 = 30000; | |
const timer$ = Rx.Observable.timer(secs30); | |
const beforeUnload$ = Rx.Observable.fromEvent(window, 'beforeunload'); | |
const getAllDocs = () => { | |
const options = {include_docs: true}; | |
return Rx.Observable.fromPromise(txDb.allDocs(options)); | |
}; | |
const logTx = row => { | |
const {doc: {type, account, amount, balance, timestamp}} = row; | |
console.log(`{${type} ${account} ${amount} ${balance} ${timestamp}}`); | |
}; | |
const logResult = (result) => { | |
if (result.total_rows < 1) { | |
console.log('No transactions'); | |
return; | |
} | |
console.log(`Rows: ${result.total_rows}`); | |
result.rows.forEach(logTx); | |
}; | |
const destroyDb = () => txDb.destroy(); | |
const logCleanUp = ({ok: isOk}) => | |
console.log(`Cleanup - account: ${isOk}`); | |
Rx.Observable.race(timer$, beforeUnload$) | |
.switchMap(getAllDocs) | |
.do(logResult) | |
.switchMap(destroyDb) | |
.take(1) | |
.subscribe(logCleanUp); | |
})(); |
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