Execute JS on AJAX submit

When a form is submitted via AJAX and it have validation errors (for example a required field is empty), I need to execute a JS file over the returned form, but I havent find a way to do it. Is there a solution to this problem?

Thanks

Hi David,

I have a script wich do some modifications over the inputs (adds placeholders and things like that). When I load the form that script is executed normally but if I send the form via AJAX and it have errors, the form returned with errors isnt affected by my script:

http://pastebin.com/SHX6qUVz

I need to execute again that script when the form has errors. I guess that the problem may be solved easily if i send the form via POST, but i need to send the form via AJAX request.

I cant show you the form cause it is in my local server :(

Thanks

Is possible to do this with gravity forms?