//手写instanceof
function myinstanceOf_(obj,class_name){
let proto=Object.getPrototypeOf(obj)
let prototype=class_name.prototype
while(true){
if(proto==null)return false
if(proto==prototype)return true
proto=Object.getPrototypeOf(proto)
}
}
var arr=[1,2]
console.log(myinstanceOf_(arr,Array))