1const privateData = new WeakMap();  
2
3class Person {  
4  constructor(name, age) {  
5    privateData.set(this, { name, age });  
6  }  
7
8  getName() {  
9    return privateData.get(this).name;  
10  }  
11
12  getAge() {  
13    return privateData.get(this).age;  
14  }  
15}  
16
17const alice = new Person('Alice', 30);  
18console.log(alice.getName());  
19console.log(alice.getAge());