To type arrays, we use generics.

Suppose you want an array to only contain numbers.

This is how you type it:

const nums: Array<number> = [1, 2, 3]

You can now add numbers to the array, but if you add a string for example you’ll have an error:

We use generics often with useState in React:

type GitHubData = {
  avatar_url: string
  name: string
  created_at: string
  bio: string
}

function App() {
  const [data, setData] = useState<GitHubData>()
}

Lessons in this unit: