Ajax vote if user not logged in

Hello,
 
I override the dwqa-single-question.js file in my site so that I can display a dialog if the user tries to vote when he’s not logged in.
 
Currently, I check for this by checking if the data returned equals zero:

success: function( data ) {
                console.log(data);
                if (data.success) {
                    parent.find('.dwqa-vote-count').text(data.data.vote);
                }
                elseif(data === 0) {
                    // show dialog
                }
            }

Is there a better way to detect if the user is not logged in when he attempted to vote?

I looked at the dwqa_action_vote function in Base.php but I don’t see where anything is returned if the user is not logged in.

Thank you