Readonly Properties

The compiler accepts the first assignment below and rejects the second, although both change a property of the same object:

class BankAccount {
  readonly accountNumber: string;
  owner: string;

  constructor(accountNumber: string, owner: string) {
    this.accountNumber = accountNumber;
    this.owner = owner;
  }
}

const account = new BankAccount("AC-1001", "Alice");

account.owner = "Alice Khan";      // Allowed
account.accountNumber = "AC-2002"; // Error

error TS2540: Cannot assign to 'accountNumber' because it is a read-only property.

The `readonly