getOwnPropertyNames does not fetch methods of Date instance

At this thread it is suggested that Object.getOwnPropertyNames should return all properties of an object including functions. But when I do the following;

let date1 = new Date();
Object.getOwnPropertyNames(date1);

this returns 0 results. But date1 has methods like date1.toISOString().

How can I fetch all those methods?

>Solution :

getOwnPropertyNames returns – as it sounds – own property names. .toISOString is not a method on the Date itself – it’s a method on the prototype.

For the same reason, the below does not log method.

class C {
  method() {}
}
const c = new C();
console.log(Object.getOwnPropertyNames(c));

Rather, they’re properties on the internal prototype of the object – Date.prototype. So, call it on the prototype:

const date1 = new Date();
console.log(Object.getOwnPropertyNames(Date.prototype));