Flow (JS)

Long ago when Angular evolved I had to decide between the new #Angular and TypeScript or React. I really love typing my code, but forced to use TypeScript was a bit too much. I prefer the new #ECMA standard and the evolution of the old and reliable JavaScript. So finding Flow (JS) was an incredible milestone in my career as a developer. Finally, I could use types in my code, and JavaScript with the new standard. I already had the experience of CoffeeScript, so TypeScript was not an option.

I use TypeScript because I tried both on a Meteor project, and found the quantity of errors it enabled us to catch and the simplification of code it allowed was higher than Flow (JS).

We use Relay because it's ability to generate Flow (JS) types based on given GraphQL fragments gives an immense amount of type safety. The relay-compiler helps us verify queries are valid before we build the app. Relay's ability to colocate queries with components, and compose many fragments, makes it easy to build a new component and get the data the component needs.

We currently use TypeScript at work. Previously we used Flow (JS) but it was sometimes really difficult to make the types work the way you want. Especially non-trivial types were problematic. And the IDE support wasn't good, Flow took too much resources and sometimes remain stuck and do not show errors (I use Visual Studio Code). With TypeScript we almost do not have these problems. IDE support is superb, working with types is much easier and typing system seems more mature and powerful. There are some downsides (like partion inheritance etc.), but TS team is still pushing it forward. So for me TypeScript is clear winner.

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