Privates in JavaScript WeakMap, medium, using WeakMap, es6

private-using-weakmap-es6.js

const _state = new WeakMap()

const _addBalance = new WeakMap()
const _logBankChange = new WeakMap()

export default class Bank {
  constructor() {
    // public variables
    this.name = 'B7'

    // private variables
    let _privateData = {
      balance: 0,
      logs: []
    }
    _state.set(this, _privateData)

    // private methods
    _addBalance.set(this, (count) => {
      _logBankChange.get(this)('add', count)

      const _privateData = _state.get(this)
      _privateData.balance += count
      _state.set(this, _privateData)
    })
    _logBankChange.set(this, (type, count) => {
      const _privateData = _state.get(this)
      _privateData.logs.push({ type, count })
      _state.set(this, _privateData)
    })
  }
  
  // public methods
  getBalance() {
    const { balance } = _state.get(this)
    return balance
  }

  addToBalance(count) {
    _addBalance.get(this)(count)
    return this.getBalance()
  }
}