[gcanti]

I wrote a library [1] and a babel plugin [2] (bonus point: is Flow compatible) in order to deal with those cumbersome runtime type checks.

[1] https://github.com/gcanti/tcomb [2] https://github.com/gcanti/babel-plugin-tcomb

[philbo]

Heh, me too: https://github.com/philbooth/check-types.js