Subj : [spidermonkey] getter/setter for all properties of an object
To   : netscape.public.mozilla.jseng
From : franck
Date : Fri Aug 05 2005 11:56 am

Hello,

I am tring to make a little object that allows me to listen all properties get and set of an object ( a kind of super watch ).
All is working properly, however I noticed that even if I defined my own setProperty, the property is stored in the object ( I can see it using a for-in loop ).
I wondering if it is possible to avoid the foo property ( in my example ) to be stored in the object.

Regards,

Franck.



c++ code:
--------

#include "jsapi.h"

JSBool ClassObjectEx_getProperty(JSContext *cx, JSObject *obj, jsval id, jsval *vp) {

   jsval getter;
   JS_GetReservedSlot( cx, obj, 0, &getter );
   jsval args[1] = { id };
   JS_CallFunctionValue( cx, obj, getter, 1, args, vp );
   return JS_TRUE;
}


JSBool ClassObjectEx_setProperty(JSContext *cx, JSObject *obj, jsval id, jsval *vp) {

   jsval setter;
   JS_GetReservedSlot( cx, obj, 1, &setter );
   jsval args[2] = { id, *vp };
   JS_CallFunctionValue( cx, obj, setter, 2, args, vp );
   return JS_TRUE;
}


JSBool ClassObjectEx_constructor(JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval *rval) {

   JS_SetReservedSlot( cx, obj, 0, argv[0] ); // getter function
   JS_SetReservedSlot( cx, obj, 1, argv[1] ); // setter function
   return JS_TRUE;
}


JSClass ClassObjectEx = {

   "ObjectEx", JSCLASS_HAS_RESERVED_SLOTS(2),
   JS_PropertyStub, JS_PropertyStub, ClassObjectEx_getProperty, ClassObjectEx_setProperty,
   JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, JS_FinalizeStub,
   JSCLASS_NO_OPTIONAL_MEMBERS
};


void InitClassObjectEx( JSContext *cx, JSObject *obj ) {

   JS_InitClass( cx, obj, NULL, &ClassObjectEx, ClassObjectEx_constructor, 0, NULL, NULL, NULL, NULL);
}

javascript code:
---------------

function ObjGetter( prop ) {
	
	//Print( 'TRACE: getter: ' + prop  );
	return ReadValueFromDb( prop );
}

function ObjSetter( prop, val ) {

	//Print( 'TRACE: setter: ' + prop + ' ' + val );
	WriteValueToDb( prop, val );
}

var obj = new ObjectEx( ObjGetter, ObjSetter );

obj.foo = 1234;

for (var i in obj ) {
	Print( i + ':' + obj[i] );
}

.