Interesting. I swear that when I previously tried this approach I had to explicitly tell typescript that a string is indeed of a particular type:

  const test(direction: Direction) => direction;
  test('up' as 'up');

But now that I'm testing in typescript playground, I no longer need to write the "as" part — simply `test('up');` works fine as well.

I wonder if you've seen this quirk of typescript before.