在javascript中，如何在类和扩展类创建的对象之间进行引用？

class MyClass {
  constructor(name) {
    this.name = name;
  }

  sayHello() {
    console.log(`Hello, ${this.name}!`);
  }
}

const obj = new MyClass("Alice");
obj.sayHello(); // 输出：Hello, Alice!

class ParentClass {
  constructor(name) {
    this.name = name;
  }

  sayHello() {
    console.log(`Hello, ${this.name}!`);
  }
}

class ChildClass extends ParentClass {
  constructor(name, age) {
    super(name);
    this.age = age;
  }

  sayAge() {
    console.log(`I am ${this.age} years old.`);
  }
}

const obj = new ChildClass("Bob", 20);
obj.sayHello(); // 输出：Hello, Bob!
obj.sayAge(); // 输出：I am 20 years old.