Extending interfaces and types

An interface or type can also be extended, but again, the syntax will differ as shown in the following code block:

// Extending an interface
interface IWork {
  company: string
  position: string
}
interface IPerson extends IWork {
  name: string
  age: number
}
// Extending a type
type TWork = {
  company: string
  position: string
}
type TPerson = TWork & {
  name: string
  age: number
}
// Extending an interface into a type
interface IWork {
  company: string
  position: string
}
type TPerson = IWork & {
  name: string
  age: number
}

As you can see, by using the & character, you can extend a type, while you extend an interface using the extends keyword.

Understanding the extension of interfaces and types paves the way for us to delve into their implementation. Let us transition to illustrating how classes in TypeScript can implement these interfaces and types while keeping in mind the inherent constraints when dealing with union types.