How to convert typescript types of strings to array of strings?

For example:

  const themeMode = ['light', 'dark'] as const;
  type MainTheme = typeof themeMode[number];
  const values = [...themeMode];

  // iterate on themeMode as const assertion => console.log(theme));

Types do not exist in emitted code - you can't go from a type to an array.

But you could go the other way around, in some situations. If the array is not dynamic (or its values can be completely determined by the type-checker at the time it's initialized), you can declare the array as const (so that the array's type is ["aaa", "bbb", "ccc"] rather than string[]), and then create a type from it by mapping its values from arr[number]:

const arr = ["aaa", "bbb", "ccc"] as const;
type myCustomType = typeof arr[number];

Here's an example on the playground.