How to add css-class active for menu items by using just javascript code?

(function($){

    $(function() { // Document Ready
        activeMenu();
    });

    // Functions
    
function activeMenu() {

    var url = window.location.pathname, 
        // create regexp to match current url pathname and remove trailing slash if present.
        urlRegExp = new RegExp(url.replace(/\/$/,'') + "$");
        // now grab every link from the navigation
        $('.menucss a').each(function(){ // Swap to your menu CSS Class or ID
            // and test its normalized href against the url pathname regexp
            if(urlRegExp.test(this.href.replace(/\/$/,''))){
                $(this).addClass('current'); // Add CSS Class 'current' to active link tag
            }
        });   
    }

})(jQuery);

Replace the “.menucss” with yours.

<ul class="menucss">
  <li><a>Home</a></li>
  <li><a>About</a></li>
  <li><a>Contact</a></li>
</ul>

That’s all!