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,        ...    }}

In my React development, I have quite a complex Babel / Webpack / Flow / Mocha toolchain set up and never had any issues with Flow. Takes some effort to set everything up (Webpack can be daunting at first), but afterwards, it just works. Flow is definitely the way to go as it is a narrower and more focused technology and as such more likely to play well with other tools. In contrast, TypeScript tries to be a lot more than just a type inference / static type checker tool and so it brings additional baggage and assumptions. So React is a specialized tool that does one thing well while TypeScript is effectively a language layered on top of JavaScript. To make sure Microsoft drives its point home, TypeScript files customarily have a different extension as well (.ts instead of .js) because you are now using a different language, got it?

TypeScript uses code generation to spit out JavaScript whereas in Flow the annotations are simply stripped off, there's no code generation as such. In the past, the Microsoft people promoting TypeScript used to make a statement to the effect that code generation is "file-local" (I don't remember the exact terminology used). This was supposed to provide a soothing reassurance that the TypeScript compiler isn't doing anything too magical. At any rate I can't find that statement prominently displayed any more. With Flow you don't need such assurances as you write in plain JavaScript (or whatever ECMA version you've configured Babel for) and the annotations are, like I said, simply stripped.

Not to mention that TypeScript is coming from a company that specializes in unethical and questionable technical practices (I don't rule out that TypeScript may eventually turn out to be the Mother of all Embrace-Extend-Extinguish ploys). Let's not forget that Microsoft did everything in their power to cause Javascript to fail as they (rightly, if belatedly) foresaw what a threat it represented, and still represents, to their crappy operating system and their bloated office suite.

Additionally, Flow's type system was much more powerful last time I bothered to evaluate TypeScript (circa 2015) and it was much easier to apply it incrementally or even sporadically in the sources. For integrating third party libraries I am using flowtyped and it is very rare that I need to complement those found there with my own definitions.

Finally, the fact that Angular uses TypeScript means absolutely nothing as Angular is not really relevant for new projects. React has won hands down, time to move on.