[ng12]

It doesn't push Flow, it just mentions it as an option. It's important to note that Flow is purely additive -- you can drop it in a project and get some use out of it. Typescript is not incremental in that way. You probably want to go all-in on it or not at all which is hard to allow for with a starter framework.

[n42]

TypeScript is now incremental in that way: https://blogs.msdn.microsoft.com/typescript/2017/04/27/annou...

[bcherny]

Have you actually used TypeScript? It's just as incremental as Flow, especially in newer versions. I converted a 100k line Coffee + ES6 codebase to TS with no issues.

[ng12]

> It's just as incremental as Flow

No, because TypeScript is a transpiler and Flow is a linter. You don't have to convert your codebase with Flow -- you can just run it on existing JS.

[bcherny]

Flow is definitely not a Linter. It is a language, like TypeScript. It also has a typechecker, like TypeScript. Unlike TS, which bundles in its own compiler, Flow relies on projects like Babel to provide a compiler. In either case, compilation is mostly as simple as first linking modules, then typechecking, then stripping away types.

You can use TS on a JS codebase as well (with the --allowJs option), or you can leave JS files to a separate build step if you don't want type inference for them. I have used both approaches in the past.

[ng12]

> Flow is definitely not a Linter. It is a language, like TypeScript

This is absolutely untrue. Have you used Flow? It runs as a completely separate process -- you're literally running Flow as a command which typechecks/lints your code. It does not do any transpilation or modify your code in any way. The only caveat is the Flow type annotations which are A. optional and B. removed at compile time without doing any typechecking. Try it some time -- you can run Flow on existing JS code without modifying either your code or your build process in any way. It'll probably even find some bugs without you needing to add additional type information. This is fundamentally different from Typescript which goes hand-in-hand with a fully-featured transpiler.

To be clear, I use TypeScript and like it a lot -- but there seems to be a persistent perception that Flow and TS are two sides of the same coin. They are not and there are certainly some use cases where Flow fits better.

[bcherny]

I have used Flow for a few projects.

I think we're saying the same thing. By "linter" I mean a program that only checks for stylistic and defined/undefined errors. To me, anything beyond that is a typechecker. Whereas TS bundles a typechecker with a transpiler, Flow keeps the 2 separate (you still need both if your program is written using Flow syntax).

You are using "linter" more broadly, which may be fair as well.

Additionally, both TS and Flow can be used on JS files with zero modification.