SDPCloud - Subject update to include custom date on form submit

Hi,

So we're creating some templates for starters/leavers and one thing I'd like is to include a custom field (start date or end date) in the subject along with the starter/leavers name. I've gotten so far, but I can't work out how to parse the custom date.

I've seen a few examples on here, but none seem to work or, are several years old.

This is my script and it works perfectly except I'm sure I need to format the date value, just not sure how to get that part working properly. I'd also like it formatted to DD/MM/YYYY

Can anyone help?

var subjectPrefix = "New Starter - "

var firstnameUDF = "udf_char5";

var lastnameUDF = "udf_char6";

var startdateUDF = "udf_date5"

var firstname = await CS.getValue("udf_fields."+firstnameUDF);

var lastname = await CS.getValue("udf_fields."+lastnameUDF);

var startdate = await CS.getValue("udf_fields."+startdateUDF);

firstname = firstname != null? firstname.trim() : "";

lastname = lastname != null? lastname.trim() : "";

CS.setValue("subject",subjectPrefix + firstname + " " + lastname + " " + "Start Date - ");

CS.end();