Re: How do I trace objects on the heap with JS 59

So, here's an actual example to clarify. Please tell me if this simple
concept is correct.

1.) On my backend objects, I set a pointer to a `new FrontEnd(cx,
rooted_obj_js)`
//----------------------------------------------
    void trace_obj(JSTracer* tracer, void* data) {
        JS::TraceEdge(tracer, (JS::Heap<JSObject*>*)data, "obj_js");
    };

    struct FrontEnd {
           FrontEnd(JSContext *cx, JS::HandleObject obj) {
               this->cx = cx;
               this->obj = obj;
               if (this->obj.get())
                   JS_AddExtraGCRootsTracer(this->cx, trace_obj,
&this->obj);
           };
          ~FrontEnd() {
               if (this->obj.get())
                   JS_RemoveExtraGCRootsTracer(this->cx, trace_obj,
&this->obj);
           };

        JSContext *cx;
        JS::Heap<JSObject*> obj;
    };
//----------------------------------------------
2.) back in the frontend (JS), I root that JSObject again like so:
//----------------------------------------------
    JS::RootedObject obj(cx, ((FrontEnd*)backend_obj->frontend)->obj);
//----------------------------------------------


3.) and in the finalizeOp of my frontend object (JS), I delete the FrontEnd
(and BackEnd) wrappers.
//----------------------------------------------
    void obj_finalize(JSFreeOp *fop, JSObject *obj) {
        auto *backend = (BackEnd*)JS_GetPrivate(obj);
        auto *frontend = (FrontEnd*)backend->obj->frontend;
        delete frontend;
        delete backend;
    };
//----------------------------------------------


Am I using the GC/tracer API correctly? I don't want to derive from
JSObject, just link the frontend and backend with wrappers. Want to know if
`JS_AddExtraGCRootsTracer`,`JS_RemmoveExtraGCRootsTracer`, and
`JS::TraceEdge` are used appropriately for this.

Hopefully this will help Miles too.

Thanks,
James