Object.getPrototypeOf and example.isPrototypeOf(obj) gave confusing results

Question

I read that Object.gePrototypeOf(someObject) returns the prototype of the passed object and aPrototype.isPrototypeOf(someObject) returns true if aPrototype is the prototype of someObject . It is obvious to me that if Object.getPrototypeOf(someObject) returns a prototype named aPrototype , then aPrototype.isPrototypeOf(someObject) will return true. But it's not happening in my code:

function person(fname, lname)
{
  this.fname = fname;
  this.lname = lname;   
}

var arun = new person('Arun', 'Jaiswal');

console.log(Object.getPrototypeOf(arun));  //person
console.log(person.isPrototypeOf(arun));   //false

What's wrong?

Answer 1

As per MDN , syntax of isPrototype is

prototypeObj.isPrototypeOf(obj)

Also refer isPrototypeOf vs instanceof

 function person(fname, lname) { this.fname = fname; this.lname = lname; } var arun = new person('Arun', 'Jaiswal'); console.log(Object.getPrototypeOf(arun)); //person console.log(person.prototype.isPrototypeOf(arun)); 

Answer 2

Prototype of arun is not person but person.prototype :

Object.getPrototypeOf(arun) === person.prototype; // true
person.prototype.isPrototypeOf(arun); // true

Answer 3

isPrototypeOf is not called on the constructor itself, but on the constructor's prototype property.

alert(person.prototype.isPrototypeOf(arun)); // true

This means that the prototype of arun is not person , but person.prototype .