對象屬性刪除

function fun(){
  this.name = 'mm';
} 
var obj = new fun();
console.log(obj.name);//mm
delete obj.name;
console.log(obj.name); //undefined

不能刪除變量

var name ='lily';
delete name;
console.log(name);//lily

即直接用delete刪除不了變量

不能刪除從原型鏈繼承的屬性

Object.prototype.a = 18;
let obj = {};
delete obj.a;//false
console.log(obj.a)//18
delete Object.prototype.a;//true
console.log(obj.a)//undefined