Person class wrote in TypeScript

person.ts

class Person {

  private name: string;
  private age: number;

  constructor(name: string, age: number){
    this.name = name;
    this.age = age;
  }
  
  advanceAge(){
    this.age++;
  }

  getAge(){
    return this.age;
  }

  passALotOftime(years: number){
    this.age += years;
  }
}

function doBirthday(citizen: Person){
  citizen.advanceAge();
  console.log(`Happy ${citize.getAge()} years!`);
}

const leonardo = new Person('Leonardo', 21); // As you can see, I don't have to explicity declare the type, because TS knows that is the Person type
doBirthday(leonardo);
leonardo.age = 21; // Note that this is not possible, because age is a private attribute
leonardo.passALotOftime('twenty'); // Neither is this, because this method expects a number, not a string