Several people advocate Object.extend() that copies only own properties. I
don't understand why; I'll make the case for copying all properties.
At a call site I use, say
foo.bar();
Ordinarily I should not be concerned about details of bar()'s
implementation. In particular I should not be concerned if bar() is own or
not.
Now I decide to create a new object from |foo|, by adding properties with
Object.extend():
var fuz = Object.extend(foo, {paper:'in', shoes:'my'});
later I write
fuz.bar();
If Object.extend() only uses own properties, the success or failure of that
statement depends upon the location of bar() in foo. While one might argue
that use of extend() is one case where devs should be concerned with details
of bar()'s implementation, how does it help in this case? If bar() is in a
prototype then I am back to manual property manipulation get the |fuz|
object I want.
If Object.extend() copies all properties (into prototype or not is a
different issue) then the resulting object acts as an extension of the one I
want to extend.
On the other side I don't see any advantage to copying only own properties.
Again I will suggest Object.getOwnProperties() as a way of providing the
answer some would like to see. Again I will point out that Object.extend()
with plain objects is not affected by these issues.
jjb
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