Subj : Re: [SpiderMonkey] Confused about class property
To   : netscape.public.mozilla.jseng
From : Peter Paulus
Date : Fri Oct 07 2005 02:56 pm

Brendan Eich wrote:
> Peter Paulus wrote:
> 
>>
>>
>> Not just to start a monologue, I've disassembled the javascript:
>>
>> var x = ColorSpace.lab;
>>
>> into:
>>
>> 00000:   0  defvar "x"
>> main:
>> 00003:   0  bindname "x"
>> 00006:   0  name "ColorSpace"
>> 00009:   0  getprop "lab"
>> 00012:   0  setname "x"
>> 00015:   0  pop
>>
>> So I guess it must be the interpreter that turns ColorSpace into a 
>> Function object, rather than an 'ColorSpace' object.
>>
>> Are there flags on my JSClass struct or otherwise to manipulate this 
>> behavior?
> 
> 
> If you don't want your call to JS_InitClass to bind a constructor to the 
> class name in the global object, pass null for the |constructor| formal 
> parameter.  Then the class name will denote a prototype object of your 
> class, containing the properties and methods (not the static properties 
> and methods) you specify.
> 
> /be
I'm not sure I want to bind a constructor. I've looked at the 
constructor as a convenient place to bind private data to an object 
(JS_SetPrivate()).

Up till now I've been passing the constructor function to JS_InitClass() 
and was still able to handle JSBool getClassProperty(JSContext*, 
JSObject*, jsid, jsval*) for any class. This has worked fine, since 
every JSClass pointed to it's own static JSBool 
getClassProperty(JSContext*, JSObject*, jsid, jsval*) function. 
Implicitely, when this function is called, you know for which class this 
is. There was never a need to examine the JSObject* in this case. Based 
on the id I could return an appropriate result.

In my current project I'm trying to build classes dynamically in 
SpiderMonkey from Adobe InDesign's ExtendScript, in order to use their 
native objects from Spidermonkey. In this setup I have exactly one 
static method: JSBool getClassProperty(JSContext*, JSObject*, jsid, 
jsval*) to serve all classes. Now I was suprised to find that JSObject* 
pointed to a "Function" object.

If I omit the constructor function with JS_InitClass() indeed the 
getClassProperty() contains the right kind of object. But then I have 
lost my place to augment a JSObject with my private data.

Can you advise me of a suitable place to add private data to a JSObject?

Am I not missing out on the constructor function in case some script uses:
var x = new ColorSpace()
var y = ColorSpace()

?

I've been trying to read the ECMA spec on this subject (section 11.2.1, 
Property Accessors). Can you elaborate on this some more, because I was 
expecting to find some reference to [Construct]?

With kind regards,
Peter Paulus

.