Programmatically set field to numeric format

I can change an Acrobat text field FROM the Acrobat 'Number' format TO the 'None' format with this script:

     var f = this.getField("num.SDebit.22");

       f.setAction('Format', "");

       f.setAction('Keystroke', "");

I would like to do the opposite: i.e. programmatically set an Acrobat text field format TO the number format and specify the number options available in the Format dialog box of text field properties .

Can this be done, and if so, how.