I've been writing js professionally for more than ten years, and I totally love flow. Sure, it doesn't happen that often that I feel like I've caught with it a

I've been writing js professionally for more than ten years, and I totally love flow. Sure, it doesn't happen that often that I feel like I've caught with it a bug I wouldn't have without it (not even sure how you can tell one from the other, when you correct a type check error), but the most notable effect is the release of tension : I don't have to double check everything I write, I can rely on the type system to report obvious problems. If anything, I think flow does not go far enough, compared to compiled languages with type systems. The fact that it allows to mix typed and non typed code is error prone, and there are annoying edge cases, like the spread variables not being correctly checked for (this can cascade quickly, when passing properties in react). I would love to see types as a core part of the language, with native browser tooling.