John Resig wrote:
> I wanted to bring up some further evidence for the widespread use of an
> extend() method.
I always need both these functions. However my ObjectClone
function is just a single statement that calls the other function:
return ObjectMerge (Source, {}). So I see Clone as trivial syntactic
sugar. Merge is necessary and costs work and processing time.
Ingvar
> 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]>, es4-discuss@mozilla.org
> 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: es4-discuss@mozilla.org; [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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--
Ingvar von Schoultz
------- (My quirky use of capitals in code comes from my opinion that
reserved and predefined words should all start with lowercase, and
user-defined should all start with uppercase, because this will easily
and elegantly prevent a host of name-collision problems when things
like programming languages are upgraded with new labels.)
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