Modern Front-End Development for Rails, 2nd Edition

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: number
  status: TicketStatus
}

And let’s say we have a data source that is unreliable and we want to make all the fields optional for data coming from that source. We could create a new type:

interface OptionalTicketData {
  id?: number
  row?: number
  number?: number
 status?: TicketStatus ...