[winterlight]

I don't know about Flow, but in Typescript you can still fire up a REPL and play around. The difference is that the typechecker validates every command you run. This is enough for small experiences, e.g., when you want to validate an algorithm. But yes, in the case you want to rerun your application to test your changes, the feedback cycle is a bit longer. But I find acceptable considering that static-typing makes refactoring significantly easier and less risky, which is important when working on large projects.