(function () {
  var activeLink = document.querySelector('.nav a.active');
  if (!activeLink) {
    return;
  }

  var links = Array.prototype.slice.call(document.querySelectorAll('.nav a'));

  function setActiveFromHash() {
    var hash = window.location.hash || '#start';
    links.forEach(function (link) {
      if (link.getAttribute('href') === hash) {
        link.classList.add('active');
      } else {
        link.classList.remove('active');
      }
    });
  }

  window.addEventListener('hashchange', setActiveFromHash);
  setActiveFromHash();
})();