class BankAccount {
  #balance;
  #transactionHistory = [];

  constructor(initialBalance) {
    this.#balance = initialBalance;
  }

  deposit(amount) {
    this.#balance += amount;
    this.#transactionHistory.push(`+${amount}`);
    return this;
  }

  withdraw(amount) {
    this.#balance -= amount;
    this.#transactionHistory.push(`-${amount}`);
    return this;
  }

  get summary() {
    return `Balance: ${this.#balance} | Transactions: ${this.#transactionHistory.join(", ")}`;
  }

  static hasPrivateBalance(obj) {
    return #balance in obj;
  }
}

const account = new BankAccount(100);
account.deposit(50).deposit(25).withdraw(30);

console.log(account.summary);
console.log(BankAccount.hasPrivateBalance(account));
console.log(BankAccount.hasPrivateBalance({}));