document.addEventListener( 'DOMContentLoaded', function() {
  var url = window.location.href;
  var navs = document.getElementsByTagName("nav")[0].getElementsByTagName("a");
  for (var i = 0; i < navs.length; i++) {
    if (url.startsWith(navs[i].href)) {
      navs[i].classList.add('active');
    }
  }
});