Take a look at the Gravity Forms developer documentation. The Gravity Forms filter gform_register_init_scripts can be used to execute custom scripts on a form. It can be implemented in your themes functions.php.
Description
Tap into Gravity Forms' "initalization scripts" functionality and register your own scripts to run inline with Gravity Forms. Scripts added via the GFFormDisplay::add_init_script() function will be output with the form(s) they are registered for.
Example (Simplified)
<?php
add_filter('gform_register_init_scripts', 'gform_my_function');
function gform_my_function($form) {
$script = '(function($){' .
'$('.gf_yourfield input').each(function(){
// do something
});' .
'})(jQuery);';
GFFormDisplay::add_init_script($form['id'], 'gform_my_function', GFFormDisplay::ON_PAGE_RENDER, $script);
return $form;
}
?>