var tom={
name:'Tom',
_birth:1999,
age:undefined
};
Object.defineProperty(tom,'age',{
get:function (){
let d=new Date();
let year=d.getFullYear();
let age=year-this._birth;
return age;
}
})
tom.age; //19
仍有一個問題,這個tom對象中的age屬性,加不加不影響效果,所以到底要不要呢?