(function($) {
    $.fn.extend({
        characterCounter: function() {
            var area = $(this);

            var counter = $('<span class="characterCount"></span>');
            var text = " merkkiä jäljellä";
            area.parent().append(counter);

            var updateCounter = function() {
                var remaining = 255 - area.val().length;
                counter.toggleClass('error', remaining < 0);
                counter.text(remaining + text);
            };

            updateCounter();
            area.bind('keyup', updateCounter);
        }
    });
})(jQuery);