Proof of Concept (recompose) - Bank-Account-System composition with higher-order functions (NodeJS6)

bank-account-system-poc.js

const account = openBankAccount({name: 'Max Muster'})({})
account.deposit(1000)
account.withdraw(800)
account.withdraw(800)
// use compose(...) building block
const { calculateBalance, name, transactions, save} = compose(withBalanceCalculation({}), withStore())(account)
console.log(`${name}: ${calculateBalance()} [${transactions.map(x => x.deposit || 0 - x.withdraw)}]`)
console.log(save())

// same stuff, but use the handy way
// const bankAccountWithBalanceCalculation = withBalanceCalculation({})(account)
// const bankAccountWithStore = withStore()(account)
// console.log(bankAccountWithBalanceCalculation.calculateBalance())
// console.log(bankAccountWithStore.save())

const transferredAccount = openBankAccount({name: 'John Doe'})(account.load(account.save()))
transferredAccount.withdraw(200)
transferredAccount.withdraw(200)
transferredAccount.deposit(500)
const transferredAccountWithBalanceCalculation = compose(withBalanceCalculation({}))(transferredAccount)
console.log(`${transferredAccountWithBalanceCalculation.name}: ${transferredAccountWithBalanceCalculation.calculateBalance()}`)

bank-account-system.js

const openBankAccount = ({name = 'anonymous'}) => ({transactions = []}) => ({
  name,
  transactions,
  deposit: amount => transactions.push({deposit: amount}),
  withdraw: amount => transactions.push({withdraw: amount}),
})

const withBalanceCalculation = ({amount = 0}) => (obj = {}) => Object.assign(obj, {
  calculateBalance: () => (obj.transactions || []).reduce((s, n) => {
    if(n.deposit) s += n.deposit
    if(n.withdraw) s -= n.withdraw
    if(s < 0) s += n.withdraw
    return s
  }, amount),
})

const withStore = () => (obj = {}) => Object.assign(obj, {
  load: data => JSON.parse(data),
  save: () => JSON.stringify(obj),
})

// compose high-order functions 
const compose = (...funcs) => funcs.reduce((a, b) => (...args) => a(b(...args)))