Console Error with Ajax: ReferenceError: $ is not defined

You need to include jquery library for that.Like this. You need to include this 1st, then write $.ajax to execute.

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

It looks like the jQuery libraries have not been included within your project.

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>