Mapped Types with Template Literals

TypeScript 4.1 added support for template literals, you can understand some of the basics in example:intro-to-template-literals 4.1 introduces new syntax inside a mapped types declaration, you can now use "as `templated string`" which can be used to transform strings inside a union. For example, this type will transform all of the properties of an existing type into four functions which correspond to traditional REST calls. Template strings literals to describe each API endpoint: 

type GET = `get${Capitalize}`
type POST = `post${Capitalize}`
type PUT = `put${Capitalize}`
type DELETE = `delete${Capitalize}`

// A union of the above literal types
type REST = GET | POST | PUT | DELETE
// Takes a type, then for each string property in the type, map that key to REST above, which would create the four functions. 
type RESTify = {
  [Key in keyof Type as REST]: () => Type[Key]
};
// The `Key extends string ? Key : never` is needed because an object can contain strings, numbers and symbols as keys. We can only handle the string cases here. Now we have a list of objects available through the API: 
interface APIs {
  artwork: { id: string, title: string };
  artist: { id: string, name: string };
  location: { id: string, address: string, country: string }
}

// Then when we have an object which uses these types
declare const api: RESTify

// Then all these functions are automatically created 
api.getArtist()
api.postArtist()
api.putLocation()
// Continue learning more about template literals in: example:string-manipulation-with-template-literals Or read the announcement blog post: https://devblogs.microsoft.com/typescript/announcing-typescript-4-1-beta/#template-literal-types