Re: JS 45 problem

On 5/24/16 12:17 PM, Kent Williams wrote:
> +        JS::RootedObject newTarget(cx,&args.newTarget().toObject());
> +        JS::RootedObject protoObj(cx);
> +        if(!JS_GetPrototype(cx,newTarget,&protoObj))

No, that's wrong.  What you want is more like:

   JS::RootedValue protoVal(cx);
   if (!JS_GetProperty(cx, newTarget, "prototype", &protoVal))
     return false;
   JS::RootedObject protoObj(cx);
   if (protoVal.isObject())
     protoObj = &protoVal.toObject();
   else
     protoObj = JS_GetObjectPrototype(cx, newTarget);
   obj = JS_NewObjectWithGivenProto(cx, &spider_xml, protoObj);

(yes, the signature of JS_GetObjectPrototype is dumb; we should fix that).

Basically, implement 
http://www.ecma-international.org/ecma-262/6.0/#sec-getprototypefromconstructor 
with the second arg being %ObjectPrototype%.

I don't think there's a more succinct API for this, sadly.  We should 
totally consider adding one; something like:

   JS::GetPrototypeFromConstructor(JSContext *cx,
                                   JSObject* ctor,
                                   JSProtoKey key);

or something.  I filed 
https://bugzilla.mozilla.org/show_bug.cgi?id=1275312 on that.

-Boris