How to have a custom subject line for email submit button?

Hello,

I am creating a form to fill out and submit for emailing, but I would like the subject line of the email to be dependent on values in the form.  Specifically, I want the submit button to execute a JavaScript to identify the value selected in 'Payroll Area', which is two possible radio button selections: Hourly or Salary, and indicate in the email subject line that the form is related to an hourly or salary submission.

Any ideas?

Thank you!