How To Validate Upload File Using Javascript

Here is my file type field and I have placed in my custom form .So I want to validate that file when user will browse any file means select any file. That event will occurred with onchange event. So I called a java script function check_photo() on onchange events.

Magento : List Of Prototype Javascript Validation Classes With Error Message

As U know there are some default classes in magento form field for validation.Like required-entry , validate-email ..etc.So I am here showing  to you all the default classes present in Magento (ver. 1.7.0.2) for  form validation .