FAILED: ReferenceError: is not defined at code example
Example 1: Uncaught ReferenceError: $ is not defined
<script src="https://code.jquery.com/jquery-1.9.1.js"></script>
<script src="path-para-seu-script"></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>