Hi there I am trying to add a simple jquery shopping cart to a site however, whatever I add doesn't seem to be picking up the js file. I have currently got shopkart on this pagedemo shop page

My code is as follows to link the js file:

<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous">
</script>

<script src="/scripts/shopkart.js"></script>

    <script>
$(function () {
    $.shopkart();
});
</script>

I have tried countless others which all work outside of Umbraco (on Dreamweaver for example) It's probably something simple, but I really can't work it out and have spent days on it already.

Thanks in advance for your help, Natasha