buttonhandler.js

$('.like-button').on('click', function(evt) {
  evt.preventDefault();
  var $btn = $(evt.currentTarget);
  $.post('/likes/ ' + $btn.data('bookmark-id'))
    .success(function(response) {
      $btn.removeClass('like-button').addClass('unlike-button');
      $btn.text('unlike');
      // Show flash message, instead probably.
      alert('You just liked something successfully');
    }).fail(function(response) {
      alert('SOMETHING WENT WRONG :(');
    });
});

$('.unlike-button').on('click', function(evt) {
// ... you get the idea, hopefully.
});