1. typeof能识别值的类型；string、number、null、undefined、boolean、obejct、function、symbol、bigint
2. instanceof用于检测构造函数的prototype是否出现在对象的原型链上

const foo = "abc"; 
console.log(tyepof foo); // 'string'

const foo2 = 123; 
console.log(tyepof foo2); // 'number'


function Bar(){}
const bar = new Bar();
console.log(bar instanceof Bar);// true
const obj = new Object();
console.log(obj instanceof Bar);// false