Subj : Equivalent of JS_InitClass for global object?
To   : netscape.public.mozilla.jseng
From : jjl@pobox.com (John J. Lee)
Date : Fri Aug 22 2003 11:07 pm

I've written a Javascript/Python bridge.  I can implement Javascript
objects in Python, except for one case: I can't implement the JS
global object in Python (in particular, I want to implement the
"window" object found in web browsers' object models).

Before, I just had this:

static JSClass global_class = {
    "MyClass", 0,
    JS_PropertyStub, // JSPropertyOp addProperty;
    JS_PropertyStub, // JSPropertyOp delProperty;
    JS_PropertyStub, // JSPropertyOp getProperty;
    JS_PropertyStub, // JSPropertyOp setProperty;
    JS_EnumerateStub, // JSEnumerateOp enumerate;
    JS_ResolveStub, // JSResolveOp resolve;
    JS_ConvertStub, // JSConvertOp convert;
    JS_FinalizeStub // JSFinalizeOp finalize;
};

JSObject *
make_global_object(JSContext *cx) {
    /* Statically initialize a class to make "one-off" objects. */
    return JS_NewObject(cx, &global_class, 0, 0);
}


and in my context initialisation code:

global_object = make_global_object(cx);
JS_InitStandardClasses(cx, global_object);


That was working fine, but as I say, I wanted to implement the methods
and properties of my global object in Python.  So, instead of a static
JSClass, I arranged to use my usual machinery for binding a proxy JS
object to Python, with a small variation.

From the point of view of the JS interpreter, my "usual machinery"
does this:

1. malloc a JSClass for the proxy.
2. Initialise the JSClass struct with stub methods, except for
   get/setProperty (which delegate to the Python interpreter).
3. JS_InitClass(
       cx, global_object, NULL, jsclass, constructor_stub, 0,
       NULL, NULL, NULL, NULL);
4. JS_DefineObject(cx, global_object, name, jsclass, NULL,
                   JSPROP_READONLY);


Obviously, 3 doesn't carry over to the case where the Python object
I'm trying to bind to JS is the JS global object itself.

So, what should I do instead?  I tried the following in place of 3 and
4 above:

3b. global_object = JS_NewObject(cx, jsclass, NULL, NULL);
4b. JS_DefineProperty(cx, global_object, name,
                      OBJECT_TO_JSVAL(global_object), NULL, NULL, 0);


So, to summarise, instead of:

global_object = make_global_object(cx);
JS_InitStandardClasses(cx, global_object);


I've now got steps 1, 2, 3b, 4b, followed by JS_InitStandardClasses,
as usual.

When I do that, though, binding another Python class (steps 1 to 3
above) stops working -- eg. if I bind a Python class named "foo" and
then evaluate this:

var f = new foo();


spidermonkey complains:

TypeError: foo is not a constructor


It seems my JS_InitClass on foo doesn't work when the global object is
created with NewObject.  Another symptom is that, though the global
object has a "window" property, it doesn't delegate to Python --
rather, I get:

TypeError: window has no properties


I don't understand that, because window was JS_DefineProperty'd to the
global object, whose class has get/setProperty functions that call
back to Python.

What am I doing wrong?


John

.