How To Make That Responsive Hamburger Menu Work? It Just Doesnt

Can you tell me why that hamburger menu doesn't open? all the files are in one folder as you can see here: jQuery is included on first position using Chromes newest version But

Solution 1:

Make sure you run the javascript code only when the document is ready-

$( document ).ready(function() {
    $('.hamburger').on('click', function(e) {
       e.preventDefault();
       $('.menu').toggleClass('slide-down');
    });
});