设置自己的instanceof

   首先我们先介绍一下instanceof的原理： instanceof主要是检测某个构造函数的原型对象在不在某个原型链上

  function myinstanceof (left,right) {
      let rightProto = right.prototype;
      leftProto = left._proto_;
      while (true) {
          if(leftProto === null ) return false;
          if(leftProto === rightProto) return true;
          leftProto = left._proto_;
      } 
  }