Opening a modal per button click ? I'm doing something wrong...

Hi I am supposed to open a modal (the content is already there) which has the id "reservemodal" with a "Reserve Table" button using javascript and bootstrap - but how I don't get it.

This is where the button is:

        <div class="col-12 col-sm align-self-center">
            <a role="button" 
            class="btn btn-block btn-sm nav-link btn-warning" 
            href="" onclick="openModal()"
            >Reserve Table
            </a>
        </div>

And this is the bit of javascript code that I included into my scripts.js file, I have tried including it inside the $(document).ready(function()) as well as outside of it:

        function openModal(){
            $('#reservemodal').modal('show'); 
     }

So the problem is that simply nothing happens after clicking the "Reserve Table" button.