uncaught referenceError: $ is not defined at video code example

Example 1: Uncaught ReferenceError: $ is not defined

make sure that your jquery script is being loaded before every other script

Example 2: Uncaught ReferenceError: $ is not defined

You should put the references to the jquery scripts first.
<script src="jquery-3.5.1.js"></script>
<script type="text/javascript" src="script.js"></script>