Jquery SELECT2未加载

Question

这是我的索引文件。

<?php
    use yii\helpers\Url;
    use yii\helpers\Html;
    use yii\bootstrap\Modal;
    use kartik\grid\GridView;
    use johnitvn\ajaxcrud\CrudAsset; 
    use johnitvn\ajaxcrud\BulkButtonWidget;

    CrudAsset::register($this);
    $this->registerJs($this->render('script2.js'), \yii\web\VIEW::POS_READY);
    ?>
    <div class="op-transaction-listing-index">
        <div id="ajaxCrudDatatable">
            <?=GridView::widget([
                'id'=>'crud-datatable2',
                'dataProvider' => $listing,
                //'filterModel' => $searchModel,
                'pjax'=>true,
                'columns' => require(__DIR__.'/_columns.php'),
                'toolbar'=> [

                ],          
                'striped' => true,
                'condensed' => true,
                'responsive' => true,    
                'resizableColumns'=>true,
                'persistResize'=>true,
                'bordered'=> true,      
                'panel' => [
                    'type' => 'primary', 
                    'heading' => '<i class="glyphicon glyphicon-list"></i> Op Transaction Listings listing',

            ])?>
        </div>
    </div>

    <?=  Html::a('Create',false,['id'=>'test','class'=>'btn btn-success pull-right'])?>

    <?php Modal::begin([
        "id"=>"ajaxCrudModal",
        "footer"=>"",// always need it for jquery plugin
    ])?>
    <?php Modal::end(); ?>

我所做的是点击表格单元格，它将删除其中的文本并添加select2下拉列表。

$(document).ready(function(){
    $('#crud-datatable2-container > table > tbody > tr:nth-child(1) > td:nth-child(2)').on('click',function(){
        $(this).text('');
        $(this).append('<select name="testing" class="form-control" id="testing"></select>');

        $('select#testing').select2();
    });
});

然后它继续显示Uncaught TypeError: $(...).select2 is not a function..这种类型的错误。我里面只有一个脚本。我哪里做错了？