HTML Help for Nav Bar

Hello everyone. I need a little help with my html code.
I want to load html file (menu.html) inside my index.html file

I am trying to achieve this using JavaScript.
Here is an example how i am trying to achieve this.

this is menu.html file

<!-- Mobile Nav (max width 767px)-->
<div class="mobile-nav">
    <!-- Navbar Brand -->
    <div class="amado-navbar-brand">
        <a href="index.html"><img src="core/img/core-img/drveniproizvodi-logo.png" alt=""></a>
    </div>
    <!-- Navbar Toggler -->
    <div class="amado-navbar-toggler">
        <span></span><span></span><span></span>
    </div>

</div>
<!-- Header Area Start -->
<header class="header-area clearfix">

    <!-- Logo -->
    <div class="logo">
        <a href="index.html"><img src="core/img/core-img/drveniproizvodi-logo.png" alt=""></a>
    </div>
    <!-- Social Button -->
    <div class="social-info d-flex justify-content-between">
        <a href="#"><i class="fa fa-pinterest" aria-hidden="true"></i></a>
        <a href="#"><i class="fa fa-instagram" aria-hidden="true"></i></a>
        <a href="#"><i class="fa fa-facebook" aria-hidden="true"></i></a>
        <a href="#"><i class="fa fa-twitter" aria-hidden="true"></i></a>
    </div>

    <div class="categories-menu">
        <a href="index.html"></a><br>
        <a href="subfolder/index.html"></a><br>
        <a href="subfolder/index.html"></a><br>
        <a href="subfolder/index.html">  </a><br>
        <a href="subfolder/index.html"></a><br>
    </div>
</header>
<!-- Header Area End -->

and this is index.html file

<html>
<head>
    <link rel="stylesheet" href="core/css/core-style.css">
    <link rel="stylesheet" href="core/style.css">
</head>
<body>

    <div id="menu"></div>

    <script>
        $(function(){
          $("#menu").load("menu.html");
        });
    </script>
</body>
</html>

The thing is, the design loads properly. But the functionality doesn't work. When i press the button to open the menu on a mobile device.
BUT when i simply paste the code from menu.html inside index.html works just fine?
Here is a picture how it looks
https://prnt.sc/h-_GWy50wOHN