SOURCE

class Person {
  constructor(){
    this.name = ""
    this.age = 0
  }
  sayName(){
    console.log('sayName')
  }
}
var o1 = new Person()
/*
3种写法,都输出name,age没有输出sayName,constructor
*/
//第1种方式
for(var prop in o1){
  console.log(prop)
}
//第2种方式
console.log(Object.keys(o1))
//第3种方式
console.log(Object.getOwnPropertyNames(o1))