Handwritten instanceof underlying principle

explain ：instanceof The principle of is to judge whether there is a prototype of the target object on the prototype chain of the object .

function myInstanace(L,R){
   let LP = L.__proto__;
   let RP = R.prototype;
   while(true){
     if(LP == RP) {return true}
     if(LP == null) {return false}
     LP = LP.__proto__
   }
}

myInstanace([1,2],Array) // true