instanceof 和 typeof

instanceof 运算符用来检测 constructor.prototype 是否存在于参数 object 的原型链

   function Person(){
       Person.prototype.dance=function(){};
   }
   function Ninja(){}
   Ninja.prototype={dance:Person.prototype.dance};
   const ninja=new Ninja();
   console.log(ninja instanceof Ninja); //true
   console.log(ninja instanceof Person);  //false
   console.log(ninja instanceof Object);  //true

  function Ninja(){}
   const ninja=new Ninja();
   console.log(ninja instanceof Ninja); //true
   Ninja.prototype={};
   console.log(ninja instanceof Ninja); //false