Simple Generic Custom Types with Typescript.ts

// Type User can have an ID which is either a number or a string
type User<CustomType extends number | string> = {
  id: CustomType
  name?: string
  age?: number
}

// In this case, we define CustomType as a string
let myUser: User<string> = {
  id: '1234-1234-1234',
  name: 'John Doe',
  age: 24,
}

// In this case, we define CustomType as a number
let myOtherUser: User<number> = {
  id: 1234,
  name: 'Jane Seymore',
  age: 48,
}