Access Modifiers

The BankAccount class from the previous lesson allows the following code, and the compiler reports nothing wrong with it:

class BankAccount {
  owner: string;
  balance: number;

  constructor(owner: string, balance: number = 0) {
    this.owner = owner;
    this.balance = balance;
  }
}

const account = new BankAccount("Alice", 100);
account.balance = -5000;
console.log(account.balance); // -5000

Any code in the program can set the balance to any number, so no single place in the code can enforce a rule such as "the balance cannot go below zero"