Why does Chrome Dev Tool show a dates __proto__ as Invalid Date?

Question

I know __proto__ is deprecated (or not part of the standard) and all that but I'm still curious as to what it means when it says Invalid Date when I look at the __proto__ value of..

var myDate = new Date(1331869050000);

Answer 1

"I'm still curious as to what it means when it says Invalid Date"

That's simply the toString value of the prototype object of the Date constructor function.

---

Date.prototype.toString(); // "Invalid Date"

---

You can override it if you like...

Date.prototype.toString = function() { return "I like turtles." };

var myDate = new Date(1331869050000);
myDate.__proto__; // I like turtles.

---

A little off topic, but __proto__ is in the current working draft for the next version of ECMAScript, codename Harmony.

http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts

• Added section B.3.1 with specifies __proto__ feature.

Answer 2

considering you made a new Date object, I wouldn't worry about it. The reason being, if you try this code:

var myDate = new Date(1331869050000);
alert(typeof myDate.getMonth != 'undefined')    //true

This will determine that you are inheriting the Date objects methods and that in fact, Date IS defined.

If you would like further investigation, take a look at this post.

Answer 3

The prototype of a Date instance has no defined value. Only the instance has a value. You define it when you instantiate it.