Yii2 when and whenClient validation

using 'whenClient' for complex client side validation 

whenClient validation 

 You have a 'Carousel' model with link, image field's When you create a 'Carousel' you choose a 'Image/gif', and follow this rule:

 ['image', 'image', 'minWidth' => 1000, 'minHeight' => 450, 'maxWidth' => 1000, 'maxHeight' => 450]

 And When you Create a 'Carousel' you choose jpg, png, then now follow this rules:

 ['image', 'image']

 In your Carousel model, use this rule:

 


public function rules() {
    return [          
        ['link', 'url'],
        ['image', 'image', 'minWidth' => 1000, 'minHeight' => 450, 'maxWidth' => 1000, 'maxHeight' => 450,
            'when' => function ($model, $attribute) {
                return (isset($model->image->type) && $model->image->type == 'image/gif');
            },
            'whenClient' => "function (attribute, value) {
                var ext = $('#carousel-image').val().split('.').pop().toLowerCase();
                    return (ext=='gif');
                }",
        ],
        [['image'], 'file', 'extensions' => 'gif,jpeg,jpg,png'],
        [['title', 'text', 'link', 'vimeolink'], 'trim'],
        ['status', 'integer'],
        ['status', 'default', 'value' => self::STATUS_ON],
        ['filebase64', 'safe'],
        [['image', 'title', 'text'], 'required', 'on' => 'create'],
        [['title', 'text'], 'required', 'on' => 'update'],                
    ];
}

'when' is server side validation it's call when you submit button (return true if valiation condition) 
AND 
'whenClient' is client side validation it's call when you choose a image file on client side (return true validation condition true).