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#10014 closed bug (wontfix)
Opened August 10, 2011 03:04PM UTC
Closed April 07, 2012 11:45PM UTC
Last modified June 17, 2013 07:45PM UTC
jQuery Extend does not properly perform a deep copy on an instance of a class
| Reported by: | anonymous | Owned by: | rwaldron |
|---|---|---|---|
| Priority: | high | Milestone: | 1.next |
| Component: | core | Version: | 1.6.2 |
| Keywords: | Cc: | ||
| Blocked by: | Blocking: |
Description
I discovered recently that performing a deep copy with $.extend does not work with classes.
If i create an object, and then assign a class to a property of that object, and do a deep copy to a new object, and change something in the original object, the new object reflects the changed value (or vice versa)
For example
function myclass()
{
this.property1 = "abc";
this.property2 = "def";
}
var a = {};
a.myclass = new myclass();
a.test = "abc";
var b = {};
$.extend(true, b, a);
alert("class Property\\na: " + a.myclass.property1 + "\\nb: " + b.myclass.property1 + "\\n\\nNormal Property\\na: " + a.test + "\\nb: " + b.test);
b.myclass.property1 = "ghi";
b.test = "def";
alert("class Property\\na: " + a.myclass.property1 + "\\nb: " + b.myclass.property1 + "\\n\\nNormal Property\\na: " + a.test + "\\nb: " + b.test);
the test property correctly has two different values after I've set one, but the prop1 of myclass always mirror each other.
I've tested this in jquery 1.4.2 and 1.6.2 in Firefox 3.6.17, IE 8, and Chrome 13
Attachments (0)
Change History (11)
Changed August 10, 2011 04:23PM UTC by comment:1
| component: | unfiled → core |
|---|---|
| owner: | → anonymous |
| status: | new → pending |
Changed August 25, 2011 07:57AM UTC by comment:2
| resolution: | → invalid |
|---|---|
| status: | pending → closed |
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Changed April 05, 2012 05:21AM UTC by comment:4
| milestone: | None → 1.next |
|---|---|
| priority: | undecided → high |
| resolution: | invalid |
| status: | closed → reopened |
Reopening per #11557
Changed April 05, 2012 05:22AM UTC by comment:5
| owner: | anonymous → rwaldron |
|---|---|
| status: | reopened → assigned |
Changed April 05, 2012 01:22PM UTC by comment:6
This strikes me as all kinds of trouble à la #8653 and #11002. The test case linked to by #11557 is in fact confirming that custom objects ''are'' copied by reference rather than recursively extended.
Deep extending of non-plain objects is better left to custom code, unless we want an endless stream of tickets about which properties/methods get copied, whether a created copy should be a plain object or new class instance, what to do to about prototypes, and so on ad infinitum.
Changed April 05, 2012 01:24PM UTC by comment:7
Amen, brother gibson042. Even ECMA punted on cloning arbitrary constructed objects.
Changed April 07, 2012 11:45PM UTC by comment:8
| resolution: | → wontfix |
|---|---|
| status: | assigned → closed |
After looking through our existing tests and the code cost this might incur, I agree 100% with gibson042 and dmethvin
There is a difference between an instance object, created by a constructor, and plain objects. The key part of the issue is this "whether a created copy should be a plain object or new class instance, what to do to about prototypes, and so on ad infinitum." from gibson042
Changed April 10, 2012 04:21AM UTC by comment:9
I suggest at least making this behaviour (limitation) explicit in the docs (http://api.jquery.com/jQuery.extend/)
Changed July 19, 2012 12:22PM UTC by comment:10
#12105 is a duplicate of this ticket.
Changed June 17, 2013 07:45PM UTC by comment:11
How about custom class instances would need to have a defined 'deepCopy' hook method which jQuery would look for and replace with whatever is returned by that method, then we can keep the logic of what to do on a copy in within the class.
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