Kostya Gorozhanov

var count = 0;
$(function() {
    count = $('input.com-check:checked').length;
    displayCount();

    $(document).on('click', 'input.com-check', function(e, a) {   
         if (this.checked) {
              count += a ? -1 : 1;
         } else {
              count += a ? 1 : -1;
         }
         displayCount();
    });
    $('#invert').click(function(e) {    
         $('input.com-check').trigger('click', true)
    });
});
function displayCount() {
    $('#count').text(count);
}