Inheriting properties from Object in JavaScript

Question

Any JavaScript object inherits its properties from Object (unless you do something like Object.create(null)). So why is the following not possible?

a={x:1,y:2}
    Object {x: 1, y: 2}
Object.prototype.isPrototypeOf(a)
    true
a.toString()
   "[object Object]"//YES, BECAUSE a INHERITS OBJECT toString() PROPERTY
a.keys()
   TypeError: undefined is not a function// BUT WHY NOT keys()
Object.keys(a)
   ["x", "y"]// WHILE THE OBJECT HAS keys() METHOD FROM ECMA5 SPECIFICATION

Based on my understanding then, the only reason it had not worked should be because keys() method is un-inheritable but I have never seen how to make some properties un-inheritable in JavaScript.

Am I missing something about how prototypical chain works?

Ry- · Accepted Answer · 2014-05-19 20:10:14Z

2

a.toString is inherited from Object.prototype.toString, not Object.toString. Object.keys is not on Object.prototype.

You could add it:

Object.prototype.keys = function keys() {
    return Object.keys(this);
};

(Don’t, of course.)

answered May 19, 2014 at 20:10

Ry-♦

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1 Comment

Jack_of_All_Trades Over a year ago

Such a nice answer and short! Thanks for clearing the confusion.

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