I have created a custom script to trigger on submission to replace the subject with 2 custom fields.  Everything is working, but how do I modify the format of the date to mm/dd/yyyy?

Custom Script:

var x=$CS.getValue("ServiceReq_15001_UDF_CHAR1");
var y=$CS.getValue("GUDF_DATE1");
var new_subject='NEW: ' + x + ' - ' + y;

if($CS.isFormSubmit()){
  $CS.setValue("SUBJECT",new_subject);
}

Thanks in advance