Catching spidermonkey copying a native object
Warrick
I'm a bit confused as to how the copying of objects work. I have
embedded a native object and that all works fine so I can do:
var v = new NativeObj();
but then if I do:
var v2 = v;
I'm not getting my native constructor called that I defined in my
jsclass structure? I want to catch the copy as I need to do 'special
native' things if the object is copied.
I'm sure I'm missing something simple!
Brendan Eich
You seem to be assuming that 'var v2' is akin to saying, in C++,
'NativeObj v2', and that the C++ counterpart-class NativeObj has a
copy-constructor.
JS is not C++. There is on deep or shallow copy on assignment. Object
is a reference type, so v2 = v just copies the reference in v into v2,
making both variables denote the same object.
If you want to copy an object, you'll need to define a copy or clone
method on it that does the right thing. "The right thing" may mean
something quite different depending on use-cases, so beware of bogus
generality.
Probably if you're embedding JS without knowing its rules, you should
get a book, and perhaps dive into the ECMA spec. The Flanagan O'Reilly
book, and Danny Goodman's JavaScript bible, or good books. The ECMA-262
Edition 3 spec is at http://www.mozilla.org/js/language/E262-3.pdf.
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