Building Mapped Types and Utility Types

In addition to limiting variables to a set of specific literal values and defining enums, TypeScript allows you to define types that are based on other types, kind of like super-powered generics. These are called mapped types. TypeScript also has a bunch of predefined mapped types that it calls utility types.

So, let’s say we have our existing type TicketData:

interface TicketData {
  id: number
  row: number
  number:

...