I agree with the point Java script dont think will be helpful here but after reading about the session ID. I feel

When a user visit a webpage a session id is created for that user, By keeping this session id as a hash session => 'true' at server.

When the user click the Like button for the first time, the session key gets changed to session => 'false' .

Now when the user refresh or click back button the session =>'fasle' remain same and thus further like count can be ignored.