Typescript string union and any string

If you ever want to create a Typescript type that provides you with autocomplete for known values but still allows any string.

You might think you can just use | string, but this actually just “clears” the other known values.

type MyString = 'a' | 'b' | string
//         ^? type MyString = string
 
type MyString2 = 'a' | 'b' | string & {}
//         ^? type MyString = "a" | "b" | string & {}

If you try and use MyString2, you’ll find it provides with autocomplete but allows other values.

Whereas MyString doesn’t provide auto-complete at all.