Configurably, always invoke for 0-arity methods.

ext/spidermonkey/js_land_proxy.c

@@ -144,7 +144,7 @@ static bool attribute_p(VALUE self, char* name)
   }
 
   return RTEST(rb_funcall(Johnson_SpiderMonkey_JSLandProxy(),
-    rb_intern("js_property?"), 2, self, ID2SYM(rb_id)));
+    rb_intern("js_property?"), 3, self, ID2SYM(rb_id), rb_method));
 }
 
 static bool indexable_p(VALUE self)

lib/johnson/spidermonkey/js_land_proxy.rb

@@ -10,9 +10,10 @@ def self.treat_all_properties_as_methods(target)
         def target.js_property?(name); true; end
       end
 
-      def self.js_property?(target, name)
+      def self.js_property?(target, name, method)
         # FIXME: that rescue is gross; handles, e.g., "name?"
-        (target.send(:instance_variable_defined?, "@#{name}") rescue false) ||
+        (Johnson::SpiderMonkey::Runtime.invoke_zero_arity? && method.arity == 0) ||
+          (target.send(:instance_variable_defined?, "@#{name}") rescue false) ||
           (target.respond_to?(:js_property?) && target.__send__(:js_property?, name))
       end
 

lib/johnson/spidermonkey/runtime.rb

@@ -19,6 +19,8 @@ def remove_gcthing(object_id)
         @gcthings.delete(object_id) if defined? @gcthings
       end
 
+      def self.invoke_zero_arity= v; @invoke_zero_arity = v; end
+      def self.invoke_zero_arity?; @invoke_zero_arity ||= false; end
 
       def current_context
         @context ||= Context.new(self)