TypeScript Classes

// TypeScript class with access modifiers
class User {
  readonly id: number;         // Cannot change after construction
  public name: string;         // Accessible everywhere (default)
  private password: string;    // Only accessible inside this class
  protected role: string;      // Accessible inside and in subclasses

  constructor(id: number, name: string, password: string, role: string = "user") {
    this.id = id;
    this.name = name;
    this.password = password;
    this.role = role;
  }

  // Public method
  greet(): string {
    return `Hi, I'm ${this.name}`;
  }

  // Private method
  private hashPassword(): string {
    return `hashed_${this.password}`;
  }

  // Protected method (accessible in subclasses)
  protected getRole(): string {
    return this.role;
  }
}

// Parameter properties — shorthand
class Product {
  constructor(
    public readonly id: number,
    public name: string,
    public price: number,
    private stock: number = 0
  ) {}
  // Properties are automatically created from constructor params!

  isInStock(): boolean {
    return this.stock > 0;
  }
}

// Getters and setters
class Temperature {
  private _celsius: number;

  constructor(celsius: number) {
    this._celsius = celsius;
  }

  get fahrenheit(): number {
    return this._celsius * 9 / 5 + 32;
  }

  set fahrenheit(f: number) {
    this._celsius = (f - 32) * 5 / 9;
  }

  get celsius(): number {
    return this._celsius;
  }
}

const temp = new Temperature(100);
console.log(temp.fahrenheit); // 212
temp.fahrenheit = 32;
console.log(temp.celsius);   // 0