fix: make Object.prototype.toString.call() work

So when Node 6+ wants to do an Object.prototype.toString call, it first
sends a query for a property (the GetToStringTag property, in
particular). Autovivify didn't know how to deal with this query, so
would bomb.

This has the property getter just return if it's asked for a
symbol. This lets v8 fall through to its own stringify routines, so an
appropriate value is emitted ("[object AutoVivify]").

This also removes the explicit toString method as the existing fall-back
one seems to work just fine.

This fixes #1

autovivify.cc

@@ -15,7 +15,6 @@ class AutoVivify : public Nan::ObjectWrap {
   Nan::Persistent<v8::Object> backing_obj;
   static NAN_METHOD(New);
   static NAN_METHOD(inspect);
-  static NAN_METHOD(ToString);
   static NAN_PROPERTY_SETTER(PropSetter);
   static NAN_PROPERTY_GETTER(PropGetter);
   static NAN_PROPERTY_QUERY(PropQuery);
@@ -78,15 +77,12 @@ void AutoVivify::Vivify(v8::Local<v8::Object> &object,
     info->GetReturnValue().Set(newobj);
 }
 
-NAN_METHOD(AutoVivify::ToString) {
-  UNWRAPOBJECT;
-  info.GetReturnValue().Set(object->ToString());
-}
-
 NAN_PROPERTY_GETTER(AutoVivify::PropGetter) {
   v8::String::Utf8Value data(info.Data());
   v8::String::Utf8Value src(property);
-  if (string(*src) == "prototype" ||
+
+  if (property->IsSymbol() ||
+      string(*src) == "prototype" ||
       string(*src) == "valueOf" ||
       string(*src) == "toString" ||
       string(*src) == "nodeType")
@@ -215,8 +211,6 @@ void AutoVivify::Init(Nan::ADDON_REGISTER_FUNCTION_ARGS_TYPE exports, ADDON_REGI
 
   tmpl->InstanceTemplate()->SetInternalFieldCount(1);
 
-  Nan::SetPrototypeMethod(tmpl, "toString", ToString);
-
   v8::Local<v8::ObjectTemplate> proto = tmpl->PrototypeTemplate();
   Nan::SetNamedPropertyHandler(proto, PropGetter, PropSetter, PropQuery, PropDeleter, PropEnumerator,
                                Nan::New<v8::String>("prototype").ToLocalChecked());

test/test-autovivify.js

@@ -69,8 +69,11 @@ describe('Autovivify', function () {
     expect(proto1).to.equal(proto2)
   })
 
-  it("has a working toString() method", function () {
-    expect(this.obj.toString()).to.equal("[object Object]")
+  it('has a working toString() method', function () {
+    expect(this.obj.toString()).to.equal('[object AutoVivify]')
+  })
+
+  it('Object.prototype.toString.call() returns an appropriate representation', function () {
+    expect(Object.prototype.toString.call(this.obj)).to.equal('[object AutoVivify]')
   })
-
 })