sortable problem

I am trying to implement a custom sortable with jquery but it does not seem to work.The code is bellow.What is wrong,the elements are not sortables,that mean that the js code does not work

<?php


$this->registerJsFile('https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js', ['depends' => [\yii\web\JqueryAsset::className()]]);

$this->registerJs("$('#sortable').sortable({

    axis: 'y',

    update: function (event, ui) {

        var data = $(this).sortable('serialize');


        // POST to server using $.post or $.ajax

        $.ajax({

            data: data,

            type: 'POST',

            url: '/your/url/here'

        });

    }

});");

?>

<ul id="sortable">

    <?php foreach ($model as $row) {?>

   <li id="item-<?php echo $row['id'] ?>"><?php echo $row['name']; ?></li>

    <?php }?>   

</ul>

[edit]It seems that I did not import the jquery-ui.js [/edit]