Uncaught ReferenceError: $ is not defined - Datepicker - Codeigniter 3

If jou want to use base_url() helper , you must load the helper in your controller:

PHP Code:

$this->load->helper('url'); 


and try (with the first slah before assets):

Code:

<script type="text/javascript" defer src="<?php echo base_url(); ?>/assets/testelib/jquery-ui.js"></script>