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

    speak() {
        console.log('Hello this is ' + this.name);
    }
}

class Child extends Person {
    // private property
    #age; // 1we can access to age property only in this class
    constructor(name, age) {
        super(name);
        this.#age = age; //2
    }
}

const child = new Child('John', 10);
child.speak()
console.log(child.name);
// 3 if try to call age, we got an error ! 
console.log(child.age);
console.log(child.#age);