封装

getter / setter

class Parent {
  constructor(name,age){
    this.name = name;
    this.age =age;
  }
   
  set age(num){
    console.log('setter')
    if(num>100){num=100}
    this._age = num;
  }
  get age(){
    return this._age;
  }
  
}

var p = new Parent("mumu",18);
p.age = 180;
p.age;
// 100