Extending union type alias in typescript?

Question

I\'m trying to limit some string fields to be only of certain values at compile time. The problem is that those values should be extendable. Here\'s a simplified example:

Answer 1

To achieve what you need, you can use intersection via the & symbol.

type Foobar = 'FOO' | 'BAR';
type FoobarBaz = Foobar | & 'BAZ'; // or: 'BAZ' | & Foobar