定时器

setInterval(()=>{
    let message = "开始学习了！" + new Date().toString()
    console.log(message)
},1000)

Object.defineProperties 双向绑定原理

    let age= 19
    let  person =  {
        name:"小米",
        sex:"女",
    }

    console.log(person)
    Object.defineProperties(person,{
        age: {
            get() {
                console.log("得到年龄");
                return age;
            },
            set(val) {
                console.log("年龄变化");
                age = val;
            }
        }
    })