How to add a drop down list?

Question

Yii

There is a drop down list

<?= $form->field($catSerial, 'id_cat')->dropDownList($cat,['prompt' => 'Выбирите категорию']); ?>

there was a need to implement the ability to add the same lists, as follows:
By clicking on any link (let's say id="dropbox"), a new drop-down list is created;
This is necessary so that the page can be displayed in two or more categories;
Specifically, this drop-down list displays the number of categories from the database.
Please tell me how to implement this correctly in Yii2.

Answer 1

Install the Select2 widget from kartik-v.
It allows multiple selections in a drop down list.
And in addition, a public property must be added to the model in order to process the preservation of the many-to-many relationship.