tutsplus_building-wordpress-themes-with-bootstrap/js/main.js

(function ($) {

  var $container = $('.portfolio-items').isotope('layout');

  $('.portfolio-filter').on('click', 'a', function (e) {
    e.preventDefault();
    $('.portfolio-filter li').removeClass('active');
    $(this).closest('li').addClass('active');
    var filterValue = $(this).attr('data-filter');
    $container.isotope({ filter: filterValue });
  });
})(jQuery);