this. tried flow, but it's too 'smart' for my iMac to handle. Flow reads all JS files without problems - which killed my iMac after using 6>gb ram. a partial solution was to manually set ignore on some node_modules packages. but still, really slow experience with atom/subl/etc.

Compared to this, typescript is actually dumb enough to require ts definition files to actually parse non-ts (js) files.