如何在TypeScript中实现类？

class Person {
  name: string;
  age: number;
}

class Person {
  name: string;
  age: number;

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

class Person {
  name: string;
  age: number;

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

  sayHello() {
    console.log(`Hello, my name is ${this.name} and I'm ${this.age} years old.`);
  }
}

const person = new Person("John", 25);

console.log(person.name); // 输出：John
console.log(person.age); // 输出：25
person.sayHello(); // 输出：Hello, my name is John and I'm 25 years old.