Suitelet Question

I have a suitelet that creates a form and attach a file to the file cabinet.
Adding file & attaching that to the job works fine.

I want to give an alert if some fields in the form are blank. Can this be done?
When I use the function,
        form.addSubmitButton('Submit')
The script added the file and attached the file to the job.

But when I used        
       form.addButton('custpage_submit', 'Submit2','submitScript()' );
the 'submitScript() function got executed, but it failed to add the file to the file cabinet.


Is there any way that I can get the url of the attached file.