[SOLVED] Calculate on the fly - but with strings

I am trying to calculate a string for a field on an ADD screen. I am using the example for calculating tax on the fly - but using my own fields and it isn't working. I am using autofill in that field also - so then I want that string and then want to add additional strings. This is what I have in Javascript on load event:

var ctrlcheckin = Runner.getControl(pageid, 'check_in_date');
var ctrlcheckout = Runner.getControl(pageid, 'check_out_date');
var ctrlsubject = Runner.getControl(pageid, 'Subject_line_for_email');
function func() {
ctrlsubject.setValue(ctrlsubject.getValue + (ctrlcheckin.getValue) +
(ctrlcheckout.getValue));
};
ctrlcheckin.on('keyup', func);
ctrlcheckout.on('keyup', func);
/
So autofill puts the employee name in subject_line_for_email and then I really want to add after that - 7/24/2019 - 7/31/2019 so that the field should be:

Joe Blow - 7/24/2019 - 7/26/2019.

I am thinking I am not doing the function correctly to get the string.