===

frappe.ui.form.on("Event", "refresh", function(frm) {

   frm.add_custom_button(__("Do Something"), function() {

       // When this button is clicked, do thisvar subject = frm.doc.subject;

       var event_type = frm.doc.event_type;

       // do something with these values, like an ajax request // or call a server side frappe function using frappe.call

       $.ajax({

           url: "http://example.com/just-do-it",

           data: {

               "subject": subject,

               "event_type": event_type

           }

           // read more about $.ajax syntax at http://api.jquery.com/jquery.ajax/

       });

   });

});