script.js

jQuery(function () {
    jQuery(".addnewpage form").each(function () {
        var $form = jQuery(this);
        var $ns = $form.find("[name='np_cat']");
        var $title = $form.find("input[name='title']");
        var $id = $form.find("input[name='id']");
        var $submit = $form.find(':submit');

console.log($ns);
        // disable submit unless something is in input or input is disabled
        if ($title.attr('type') === 'text') {
            $submit.attr('disabled', 'disabled');
            $title.on('input', function () {
                if ($title.val().length > 0) {
                    $submit.removeAttr('disabled');
                } else {
                    $submit.attr('disabled', 'disabled');
                }
            });
        }
console.log($ns);
        // Change the form's page-ID field on submit
        $form.submit(function () {
            // Build the new page ID and save in hidden form field
            var id = $ns.val().replace('@INPUT@', $title.val());
            $id.val(id);
            // Clean up the form vars, just to make the resultant URL a bit nicer
            $ns.prop("disabled", true);
            $title.prop("disabled", true);

            return true;
        });

    });
});