Thanks for the response. TypeScript definitely seems to be the community favorite, and availability of third-party type definitions is definitely an important c

Thanks for the response. TypeScript definitely seems to be the community favorite, and availability of third-party type definitions is definitely an important concern. Will definitely take a look at apollo-codegen. Though now I'm curious how the two systems differ, if at all, in their handling of third party libraries that _lack_ type definitions? From slackingoff2017's response below, it sounds like Flow might handle this scenario a bit more gracefully by still providing some level of static checks, whereas TypeScript would give up on checking any usages of the library altogether, correct? > Generative testing from types in TypeScript isn't something I've seen. With a static type system, if the code compiles then you know it's correct with respect to the types - no amount of automated testing would prove otherwise. In a dynamic language like Clojure where there are no types then you need generated values and tests to try and get some (still incomplete) safety. So you want a rich type system which can capture as much information about your data as possible - TypeScript does a nice job of this, on the whole . It's certainly true that in a static type system, generative testing can't derive any value from the types alone, and both Flow and TypeScript are static type systems. That was probably the wrong way to frame my question. I guess what I'm trying to ask is if there's a runtime property specifications system for JavaScript, similar to Clojure Spec, that can specify more than just properties of a system that are statically provable, and can test those specifications using a generative approach.