[mediumdeviation]

Enums are not JavaScript, and I've never heard of an Enum stage X proposal.

[sbjs]

Oh, you're right!

http://www.typescriptlang.org/play/#src=enum%20Direction%20%...

And yeah this could be valid JavaScript too, having nothing to do with types, but it's not in JS, only TS.

That said, it is a very cool and clever way to set k=v and v=k in an object at the same time!