Flow offers some interesting control over things like optional types (nullable) and intelligent understanding of type tests in conditionals or calls to libraries like invariant. I&#x27;ve had these sorts of features catch quite a few bugs in my editor before even running a single test.<p>Flow is also based on a daemon which continuously monitors your code. As such, it incrementally checks your modules allowing it to be extremely fast once started.<p>I ended up using flow since it fit with the language feature set I was using with Babel (JSX in react code being one example). Since then, I&#x27;ve grown to enjoy the flow based typing and the rather good support for optional and non-optional types.<p>Looking at the code lately seems to show some interesting stuff in the pipeline too. Taint tracking seems like a very useful one that I&#x27;d love to implement and seems like a natural extension of the code-flow based type system.<p>Flow could definitely use more documentation and more example code but I found the community on IRC extremely helpful and polite so perhaps it&#x27;s not a bad time to start if you&#x27;re willing to do a little reading on the site first: <a href="http:&#x2F;&#x2F;flowtype.org&#x2F;docs&#x2F;getting-started.html" rel="nofollow">http:&#x2F;&#x2F;flowtype.org&#x2F;docs&#x2F;getting-started.html</a>