Object.getOwnPropertyNames() vs Object.prototype.hasOwnProperty()

Question

Both of these obviously do similar things but my question is why is one on the prototype and one on the Object?

For example, both of these called differently. Is there a logical reason why this is the case?

var o = {name: "value"}

o.hasOwnProperty("name") //true

Object.getOwnPropertyNames(o); //name 
//Couldn't the above have been coded so we can run o.getOwnPropertNames();

Thanks.

Similar by having to do with property names. – KingKongFrog Mar 18 '14 at 20:31 — KingKongFrog, Mar 18 '14 at 20:31

score 0 · Answer 1 · edited May 23 '17 at 11:58

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The problem with adding these methods to the prototype is taht they are prone to getting overloaded.

var o = {};
o.getOwnPropertyNames = 17;
//What now?

In fact, you would often see people doing

Object.prototype.hasOwnProperty.call(o, propname);

in order to avoid the overloading issue with hasOwnProperty.

edited May 23 '17 at 11:58

Community

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answered Mar 18 '14 at 20:24

hugomg

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So then why is `hasOwnProperty` on the prototype? – KingKongFrog Mar 18 '14 at 20:26
For no good reason to be honest. Its just that we can't "fix" it now without breaking backwards compatibility. – hugomg Mar 18 '14 at 20:28
Really? I'll try to control my urge to downvote for a bit though. – sabof Mar 18 '14 at 20:28
@KingKongFrog: Because that's how it was designed at first, and had to stay for backwards compatibility. – Bergi Mar 18 '14 at 20:34
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Actually it does seems that no new object methods where introduced since ES3. – sabof Mar 18 '14 at 20:54

Object.getOwnPropertyNames() vs Object.prototype.hasOwnProperty()

1 Answers1