It's very ugly, but not crazy. Unfortunately, it misses the point: typing is about having an automated tool report on type incompatibilities. No convention can

It's very ugly, but not crazy. Unfortunately, it misses the point: typing is about having an automated tool report on type incompatibilities. No convention can fix that because you can easily not follow it (accidentally or otherwise). I would guess that in JavaScript you can get to a point similar to Python of old with Zope3 Interfaces, without needing to resort to a precompiler (though Python's decorator syntax makes thing nicer).