static void LogCallback(const v8::FunctionCallbackInfo<Value>& args) { if (args.Length() !=1) return ; Log* log = Unwrap<Log>(args.Holder()); Handle<Value> msg_value = args[0]; v8::String::Utf8Value msg_str(msg_value); log->LogMsg(std::string(*msg_str, strlen(*msg_str))); }