Subj : Re: Properties not defined with JS_DefineProperty possible?
To   : Thomas Sondergaard
From : Brendan Eich
Date : Sat Jan 15 2005 06:03 pm

Thomas Sondergaard wrote:
> On Sat, 08 Jan 2005 14:06:46 -0800, Brendan Eich wrote:
> 
> 
>>Of course -- JSClass.getProperty and JSClass.setProperty can mirror 
>>changes from and to your std::map.  You can set the JSClass.flags bit 
>>JSCLASS_SHARE_ALL_PROPERTIES to avoid any parallel map being managed by 
>>SpiderMonkey.  Then for each get or set, the appropriate JSClass hook 
>>will be called and you can fetch or store using your map.
> 
> 
> Hi Brendan,
> 
> Yes, I realize that I don't have to keep *values* in sync and that I can
> have spidermonkey invoke the get/setProperty (JSPropertyOp) to get/set the
> value from my native object, but can I avoid having to tell spidermonkey
> what properties (names!) exist up front with
> JSDefineProperty/JSDefineProperties?


Certainly.  Did you try using JSClass.getProperty?  It will be called 
for any property get on objects of that class, whether the property is 
predefined or not.


> As an example, let's say I have defined an object called 'data' and I want
> the properties on it to reflect the contents of my c++ std::map<string,
> string>. So if the expression "data['noOfImages']" (or "data.noOfImages")
> is evaluated how does the js engine know which jsid to pass to my
> getPropertyOp


JSClass.getProperty takes a jsval id, not a jsid -- are you hacking with 
JSObjectOps, or just trying to follow the internals?

Playing around with the "it" object in the js shell, setting it.noisy = 
true first, should be enlightening.


> if I have not previously told the engine that the object has
> a property with that name using JSDefinePropert*? Is this possible? What
> I'm thinking of is a hook that the engine will call to lookup properties
> on an object dynamically.


The hooks you need already exist.

/be

.