php -选择dropdownlist后ajax更新文本字段不起作用(yii)

<?php
use yii\helpers\Html;
use yii\helpers\Url;
use yii\widgets\ActiveForm;
?>

<?php $form = ActiveForm::begin(); ?>

<?= $form->field($model, 'dropdown')->dropDownList($options, ['prompt' => '请选择', 'id' => 'dropdown']) ?>

<?= $form->field($model, 'text')->textInput(['id' => 'text']) ?>

<?php ActiveForm::end(); ?>

<script>
$(document).ready(function(){
    $('#dropdown').change(function(){
        var selectedOption = $(this).val();
        $.ajax({
            url: '<?= Url::to(['site/update-text']) ?>',
            type: 'POST',
            data: {option: selectedOption},
            success: function(response){
                $('#text').val(response);
            }
        });
    });
});
</script>

<?php
namespace app\controllers;

use Yii;
use yii\web\Controller;

class SiteController extends Controller
{
    public function actionUpdateText()
    {
        $option = Yii::$app->request->post('option');
        $text = $this->generateText($option);
        return $text;
    }

    private function generateText($option)
    {
        // 根据选项生成文本字段的内容
        // 这里可以根据实际需求进行处理
        return '更新后的内容';
    }
}