Classes and Object-Oriented TypeScriptLesson 5.1

TypeScript class basics access modifiers public private protected

class declaration, constructor syntax, public modifier, private modifier, protected modifier, readonly modifier, parameter properties

Access modifiers

TypeScript adds access control keywords absent from standard JavaScript:

class BankAccount {
  public  owner: string;
  private balance: number;
  protected accountType: string;
  readonly id: string;

  constructor(owner: string, balance: number) {
    this.owner       = owner;
    this.balance     = balance;
    this.accountType = "checking";
    this.id          = crypto.randomUUID();
  }

  deposit(amount: number): void {
    this.balance += amount;
  }

  getBalance(): number {
    return this.balance;
  }
}

Parameter properties shorthand

Declare and assign constructor params in one line:

class User {
  constructor(
    public  name: string,
    private email: string,
    readonly id: number
  ) {}
}
// Equivalent to declaring and assigning all three in body

Access modifiers are compile-time only — JavaScript's private fields (#) provide actual runtime privacy if needed.