ES6 AOP Wallet

wallet.es6

class AOP {
  static extend(target) {
    Object.assign(target, AOP.prototype);
  }
}

AOP.prototype.before = function (property, fn) {
  let oldProperty = this[property];
  this[property] = function () {
    fn.apply(this, arguments);
    return oldProperty.apply(this, arguments);
  }
}
  
AOP.prototype.after = function (property, fn) {
  let oldProperty = this[property];
  this[property] = function () {
    oldProperty.apply(this, arguments);
    return fn.apply(this, arguments);
  }
}



class Wallet {
  constructor (initialAmount) {
    this.amount = initialAmount || 0;
  }
  
  add (amount) {
    this.amount += Number(amount) || 0;
  }
  
  remove (amount) {
    this.amount -= Number(amount) || 0;
  }
}

class WalletWithStorage extends Wallet {
  constructor (...args) {
    AOP.extend(this)
    super(...args);

    this.after('add', this._store);
    this.after('remove', this._store);
  }
  
  _store () {
    localStorage.setItem('amount', this.amount);
  }
}