*   1. typeof null => "object"  但是null并不是对象
 *   2. 基于typeof无法细分出当前值是普通对象还是数组对象等，因为只要是对象数据类型，返回的结果都是"object"

//数值类型
let number = 1;
console.log(typeof number) //=>‘number‘
//字符串类型
let number1 = ‘123‘;
console.log(typeof number1) //=>‘string
//boolean类型
let number3 = true; 
console.log(typeof number3)‘ //=>‘boolean‘
//null
console.log(typeof null) //=>‘object‘
//NaN
console.log(typeof NaN)//=>‘number‘
//undefined
console.log(typeof undefined)//=>‘undefined‘

//对象
console.log(typeof {})//=>‘object‘
//数组
console.log(typeof [])//=>‘object‘
//正则
console.log(typeof /^/)//=>‘object‘
//函数
console.log(typeof function(){})//=>‘function‘

 console.log(typeof typeof typeof []);
//=> typeof [] => "object"
//=> typeof "object" => "string"

result = variable instanceof Constructor