Zend Form validate with DOJO

i'm working on a Zend Form and i need to validate it client side. I need to validate Zend_Form_Element_File to have a max size and defined filetype. How i can do this? In our project we have also DOJO included. I'm new to this project so i want to understand how to use Dojo or if i use javascript or other method to do this.

My element is like this

$element = new Zend_Form_Element_File('testprint');
$element->setLabel('Allega il test print* ');
$element->addValidator('Count', false, 1); // ensure only 1 file
$element->addValidator('Size', false, 512000); // limit to 500K
$element->addValidator('Extension', false, 'jpg,png,gif'); /
$this->addElement($element);

But this validator is only for server side. I need client side