class Account {
  #balance = 0;                // private field
  currency = "BDT";           // public field

  constructor(owner, opening = 0) {
    this.owner = owner;       // instance property
    this.deposit(opening);    // call method
  }

  deposit(amount) {           // instance method
    this.#balance += amount;
  }

  get balance() {             // getter
    return this.#balance;
  }

  set balance(v) {            // setter (validate)
    if (v < 0) throw new Error("negative");
    this.#balance = v;
  }

  static bank = "BNL Bank";   // static field
  static from(user) {         // static factory
    return new Account(user, 0);
  }
}

class Savings extends Account {         // inheritance
  constructor(owner, opening, rate = 0.05) {
    super(owner, opening);              // call parent constructor
    this.rate = rate;
  }
  accrue() {
    this.#balance = this.balance * (1 + this.rate); // via getter or internal logic
  }
}