<?php
$script = <<< JS
    $('#select_img').scroll(function(e) {
            alert(1);
        });
JS;
$this->registerJs($script, yii\web\View::POS_READY);
?>

<?=
    $form->field($model, 'select_img')->dropDownList($data_select, [
        'options' => ['value' => 'none',
            'class' => 'prompt',
            'label' => 'Select']
    ])
    ?>