I wanted to bring up some further evidence for the widespread use of an
extend() method. Here are the top 5 JavaScript libraries and their associated
versions of "Object.extend()":
== jQuery.js:
(jQuery also does deep extend - but that isn't relevant here.)
jQuery.extend = jQuery.fn.extend = function() {
var target = arguments[0] || {}, i = 1, length = arguments.length,
options;
if ( typeof target != "object" && typeof target != "function" )
target = {};
if ( length == i ) {
target = this;
--i;
}
for ( ; i < length; i++ ) {
if ( (options = arguments[ i ]) != null ) {
for ( var name in options ) {
target[ name ] = options[ name ];
}
}
}
return target;
};
== Prototype.js:
Object.extend = function(destination, source) {
for (var property in source)
destination[property] = source[property];
return destination;
};
== Mootools.js:
var $extend = function(){
var args = arguments;
if (!args[1]) args = [this, args[0]];
for (var property in args[1]) args[0][property] = args[1][property];
return args[0];
};
== Dojo Toolkit:
dojo._mixin = function(obj, props){
var tobj = {};
for(var x in props){
if(tobj[x] === undefined || tobj[x] != props[x]){
obj[x] = props[x];
}
}
// IE doesn't recognize custom toStrings in for..in
if(d["isIE"] && props){
var p = props.toString;
if(typeof p == "function" && p != obj.toString && p !=
tobj.toString &&
p != "\nfunction toString() {\n [native code]\n}\n"){
obj.toString = props.toString;
}
}
return obj; // Object
}
dojo.mixin = function(obj){
for(var i=1, l=arguments.length; i<l; i++){
d._mixin(obj, arguments[i]);
}
return obj; // Object
}
== Yahoo UI:
YAHOO.lang.augmentObject = function(r, s) {
if (!s||!r) {
throw new Error("Absorb failed, verify dependencies.");
}
var a=arguments, i, p, override=a[2];
if (override && override!==true) { // only absorb the specified
properties
for (i=2; i<a.length; i=i+1) {
r[a[i]] = s[a[i]];
}
} else { // take everything, overwriting only if the third parameter is
true
for (p in s) {
if (override || !(p in r)) {
r[p] = s[p];
}
}
L._IEEnumFix(r, s);
}
};
There are a couple points that are very important here:
1) They all extend the base object with the enumerable properties at least one
other object.
2) There is very little done to prevent properties coming in from
[SomeObject].prototype - this is mostly because libraries opt not to use
.hasOwnProperty() in favor of speed and/or cross-browser compatibility (older
versions of Safari and IE Mac don't have hasOwnProperty).
3) A couple of the implementations take multiple source objects with which to
extend the base object.
The implementations in the libraries don't deal with nearly as many edge cases
as they should (such as the aforementioned hasOwnProperty - or getters and
setters) which is something that can be done in a language implementation. A
language implementation of .extend() should certainly also allowing
non-enumerable properties to be extended, as well (considering that this wont
be possible - or will be very difficult to implement - from a pure-script
perspective).
While Object.clone will certainly be useful in, and of, itself - it's not a
replacement for an extend method.
I have a pure-JavaScript version of Object.extend() that I'm working on - and
I'm building a test suite for it, as well (to make sure all edge cases are
properly defined and handled):
http://ejohn.org/files/object-extend.js
I'll be updating this file throughout the day. I'll post back when I feel as if
I have a reasonable test suite.
--John
----- Original Message -----
From: "Allen Wirfs-Brock" <[EMAIL PROTECTED]>
To: "Robert Sayre" <[EMAIL PROTECTED]>, "Mark S. Miller" <[EMAIL PROTECTED]>
Cc: "es3 x-discuss" <[EMAIL PROTECTED]>, [email protected]
Sent: Wednesday, July 16, 2008 7:10:21 PM GMT -05:00 US/Canada Eastern
Subject: RE: ES3.1 Object static methods rationale document
As far as I can recall, we didn't discuss a specific formulation that
corresponds to Object.extend but we have considered (and arguably provided)
pretty much equivalent functionality in our proposal. I assume that at least
Doug, Adam, or Kris were specifically aware of Object.extend and would have
broad it up if it was relevant. One reason, it probably wasn't was that the
starting point of our design was the full reification and control of properties
and their attributes rather than just copying properties. By the time we got
around to cloning/copying issues we already had establish some core elements of
our overall design.
Doing a bit of search I've found several different variants of the extend
function. Some are defined on Object, some on Object.prototype. Some use a
single source object and some use multiple source objects. What they all seem
to have in common is that they copy the enumerable methods from one (or more)
object to another.
The most common use case seems to be the one where the target object is a newly
instantiated object without any properties of its own. That use case (at least
for variants of extend that only take a single source object) is most directly
supported by the Object.clone function in our proposal. However, Object.clone
is defined to be a more comprehensive object duplication process than is
performed by extend. It duplicates all own properties and their attributes and
any internal properties such as its [[Value]] property if it has one.
I have personally considered whether there should be some sort of mechanism to
filter the properties copied by Object.clone. For example, you might only copy
non getter/setter properties, or only enumerable properties, or perhaps filter
out ReadOnly properties. However, I never proposed any of these for the ES3.1
spec. because I have yet to find a use case that was sufficiently compelling or
pervasive enough to justify making the interface to Object.clone more complex
(in contrast, see the explanation in the rationale document for why we added a
second argument to Object.create). If you want to do that sort of filtering
you can do it using Object.wontbecalledgetProperty and Object.defineProperty.
If you just want a fast and comprehensive copy use Object.clone.
The other obvious use case would seem to be adding some "mix-in" behavior to an
object (some of the descriptions of extend on the web call this "inheritance"
but it's not how I'd use that term). This use case is fairly directly
supported by Object.defineProperties although it is formulated somewhat
differently.
As I mention in our rationale document, this design isn't just a set of
individual functions but an attempt at a unified design where we have tried to
distribute the functional elements across of set of related functions that
often have multiple uses. Object.extend is a fine function, particular when
viewed from the perspective of what can be accomplished using the available ES3
APIs. However, it isn't something I would simply add as whole cloth to the set
of functions we have already worked out. That would mostly just added
redundant functionality and in a manner that wasn't particularly consistent
with the other functions we have defined. Instead, if we added it we would
potentially refactor the functionality of all of the proposed static Object
functions to make them stand together as a unit. I'd be happy to discuss
additional use cases to see try to see if we can find any significant hole in
our proposal.
Finally, I want to say that my approach to a situation like this where there
appears to be multiple versions of a similar but not identical function is not
necessarily to pick one and make everybody else conform. Instead, I like to
approach the problem from the perspective of what would have made these various
functions unnecessary and what primitives would have been useful in
implementing the assorted variations. If I can provide that then future users
are unlikely to need to use the old forms and existing user can migrate by
continuing to use their old API but perhaps reimplementing them using the new
primitives.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Robert Sayre
Sent: Wednesday, July 16, 2008 2:17 PM
To: Mark S. Miller
Cc: [email protected]; [EMAIL PROTECTED]
Subject: Re: ES3.1 Object static methods rationale document
Maybe someone could just give the rationale for leaving out Object.extend?
Douglas Crockford wrote that it was considered, but I'm confused since
it looks like you haven't even seen a proposal, and didn't participate
in the discussion to exclude it.
- Rob
2008/7/16 Mark S. Miller <[EMAIL PROTECTED]>:
> On Wed, Jul 16, 2008 at 10:11 AM, Brendan Eich <[EMAIL PROTECTED]> wrote:
>>
>> And? The doc gives rationales for design decisions. What's the
>> rationale for leaving Object.extend out?
>
> If the document needs to give rationales for leaving out each thing we did
> not include, it would be quite a long document. What is the argument for
> adding Object.extend()? A pointer to Resig's message or a prior discussion
> is an adequate response.
>
> --
> Cheers,
> --MarkM
> _______________________________________________
> Es3.x-discuss mailing list
> [EMAIL PROTECTED]
> https://mail.mozilla.org/listinfo/es3.x-discuss
>
--
Robert Sayre
"I would have written a shorter letter, but I did not have the time."
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