thanks for the explanation!
-----Original Message-----
From: prototype-scriptaculous@googlegroups.com
[mailto:prototype-scriptaculous@googlegroups.com] On Behalf Of T.J. Crowder
Sent: Tuesday, October 18, 2011 6:52 PM
To: Prototype & script.aculo.us
Subject: [Proto-Scripty] Re: Why created object is not extended with Object
methods?
On Oct 18, 3:08 pm, buda <www...@pochta.ru> wrote:
> T.J. what the reasons not to make them Object.prtototype methods?
If you add something to `Object.prototype`, it shows up on *every* object.
So for instance:
Object.prototype.foo = function() {
return "bar";
};
var a = {};
console.log(typeof a.foo);
// -> "function"
for (var name in a) {
console.log(name);
}
// -> "foo"
To put it mildly, this causes a problem because people expect a blank object
to be, um, blank. And in fact, you see people repeatedly running into
problems with Prototype's additions to `Array.prototype` because they're
using `for..in` incorrectly[1][2]. Compare the output of this page:
http://jsbin.com/ajiyal
with this one:
http://jsbin.com/ajiyal/2
The code is identical in the two pages, it's just that the second one
includes Prototype and the first one doesn't. Since Prototype adds a bunch
of `Array.prototype` properties, they show up on that naive
(broken) `for..in` loop.
As of ECMAScript5 it's possible to put properties on `Object.prototype` (and
`Array.prototype`) that *won't* break naive `for..in` loops by using
`Object.defineProperty` and setting `enumerable` to `false`, but there's
still the problem that people expect a blank object to be blank. And so if
(for instance) you put a `keys` property on `Object.prototype` that refers
to a function that returns the object's keys, but I have code where I use a
`keys` property on an object to mean something else entirely (very likely,
and in fact I *have* done it), there's a problem. For that reason, the list
of properties defined for `Object.prototype` in the spec[3] is very short
and likely to stay that way, in favor of properties defined on `Object` that
you pass an instance into (like `Object.keys`).
[1] http://blog.niftysnippets.org/2010/11/myths-and-realities-of-forin.html
[2] http://api.prototypejs.org/language/Array/
[3] http://es5.github.com/#x15.2.4
HTH,
--
T.J. Crowder
Independent Software Engineer
tj / crowder software / com
www / crowder software / com
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