1. Setting up with Babel: (note that if you are already using the "react" preset you don't have to do anything)
$ npm install --save-dev babel-plugin-transform-flow-strip-types
{ plugins: ["transform-flow-strip-types"] }
$ npm install --save-dev eslint-plugin-flowtype-errors
{ plugins: ["flowtype-errors"] }
We're trying to integrate more with tools like this so you don't have to go changing your entire workflow. It shouldn't be so hard to add types to your existing JavaScript code.
EDIT:
Ah I think I get it, it's for editors that don't interface with Flow but only with eslint. Well, since WebStorm has Flow support - even though it's new and there are a few tickets open - I guess I should stick with the plugin that I already chose.
So I had enough and started with Flow on one file, then two - then I spent a week converting everything to Flow. I actually found a few subtle bugs in my code, but also two or three minor ones in Flow (issues submitted). I also found clear limits for this type system, for example, when you clearly know 100% sure that a value cannot be undefined but Flow insists you add a type check before using the property because it does not follow your dynamic logic, only its types.
You actually wrap the type annotations in comments and flow will recognize them. You can use the source with the type comments in your browser!
As an example, the flow checker will read the annotations from `function f(n/:number/, s/:string/) { ... }` but since they are commented in the source code your JS engine ignores them.
This is amazing for typing existing code, since at every step you are merely inserting comments into your code. And your existing minification step will strip them out :)