productively
You missed the most important word.
As someone who has spent quite some time on Javascript codebases its amazing how quickly things break down when you get developers of different levels working on the same codebase. Optional typing allows a whole batch of problems to be caught way before weird errors/exceptions client-side. Productivity goes way up when the tooling can check basic errors.
(Part of me still wishes Haskell was an option for web scripting but I can dream)