window.onload = function() {
 $url = window.location.href;
 $links = document.querySelectorAll(".nav-link");
 $home = 'https://'+window.location.hostname+'/';
 $('.nav-item').removeClass('active');
 if ($url == $home) {
  $home_link = document.querySelector('a[href="/"]');
  $home_link.parentElement.classList.add('active');
 } else {
  for ($i = 1; $i < $links.length; $i++) {
  if($url.startsWith($links[$i])){
   $links[$i].parentElement.classList.add('active');
   }
  }
 }
}

It works untill there are some parameters in the url. Maybe someone has already solved this issue or can improve my code so it will also work if there are parameters in the url.

Thank you very much.

 

Also I would be very thankful if there are some advices or workflow tutorials for using mdb for wordpress. So I could get ahead faster with my development. The tutorials on mdbootstrap.com for wordpress are very helpful. Thank you guys again.