ReferenceError: $ is not defined

F12查看問題，發現jquery加載速度太慢

<script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.min.js"></script>

 

換了源秒加載

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>