ES 对象 有2个属性 constructor 和 __proto__
ES函数也分属对象，特有属性 prototype
function demo(){
this.id = 2
}
console.log(demo.prototype)
console.log(demo.constructor)
console.log(demo.__proto__)
var fn = new demo()
console.log(fn)
console.log(fn.constructor)
console.log(fn.__proto__)
fn.__proto__ ==demo.prototype