These use cases drop in time and again: checkbox lists; live login validation; dynamic form rows; server-side processing progress indicators; list reordering using drag and drop; and more… As always, there are a lot of terrible ways to achieve those, several decent ones, and precious few really good takes. This session will review several such use cases and detail various ways to implement them, contrasting the ugly and the beautiful, showing useful reflexes and rules of thumb, with a special focus on performance and maintenance.