Datepicker passing values to it?

Datepicker passing values to it?

I'd like to pass a value to the datepicker.  How would I do that?  When datepicker closes the calendar after I choose a date I want to execute a function with that variable below.
 
  1. $( "#CallBackDateandTime" ).datepicker({
             changeMonth: true,
             changeYear: true,
             onClose: function(dateText) { 
             Update(this.id,dateText, xx);
       }




  2.   });