Flow – A static type checker for JavaScript

Comments moved to https://news.ycombinator.com/item?id=8625222. We'll keep that one as the canonical post because it gives more background.

In case anybody's wondering, the experiment of merging threads manually like this has worked well enough that we've decided to work on building it into the system. It'll take a while to implement, though, because it's connected to a bunch of other things we're working on.