React - using TypeScript vs Flow vs?

I'm going to start this answer saying that I have never used Flow, so I can't say much about it. But, we are using React and TypeScript at work and it works great.

We have all the benefits I imagine you already know about, like refactoring, type safety, autocompletion, etc.

Sure, for what I have seen, the Flow syntax is cleaner than TypeScript, but you can add your types using TypeScript incrementally. I think, this is more a matter of taste. Some people prefer to have the code explicitly typed, others prefer to type less and have a stronger type inference.

About, the technologies I'd say TypeScript is a safe bet, Microsoft is pushing the language (there will be a version 2 soon), Angular is using it as well and there are a lot of Angular developers. Even here on SO, the tag TypeScript has more than 4K followers and it's rare to have an unanswered question.

The big issue with TypeScript, at least for us is that from time to time, we decide to use a component or a library that does not have the type definitions, so we have to create them ourselves. But I guess, that's a way to contribute back to the community.

I just asked myself the same question (though not with React) and found the following articles useful in evaluating the two:

• http://michalzalecki.com/typescript-vs-flow/ (2016-07-15)
• https://blog.wearewizards.io/flow-and-typescript-part-2-typescript (2015-11-20)
• https://blog.wearewizards.io/flow-and-typescript-part-1-flow (2015-11-13)

The approach taken by the flow designers feels more functional with better type inference and a better approach for nulls. However, TypeScript has better community support especially with respect to pulling in types for third party libraries via http://definitelytyped.org/ which is important for having types flow through all your code for maximum type safety. TypeScript is created by Microsoft which has a rich history in writing compilers and evolving the technology in favorable directions - notable here is C# and the fact that they are already adding non-null types (2016-07-11): https://blogs.msdn.microsoft.com/typescript/2016/07/11/announcing-typescript-2-0-beta/

TypeScript seems like the safer bet today.

And for those trying TypeScript out in an existing codebase I found the following settings in my tsconfig.json file really helpful in allowing TypeScript to co-exist nicely with JavaScript (allowing transition one file at a time):

{
    "compilerOptions": {
        "allowJs": true,
        "isolatedModules": true,
        ...
    }
}