I have looked at Flow. I have to admit, I am biased toward good-looking code. Unless you use something like LightScript[0], Flow's syntax is not as clean or straightforward as that of TS.

Edit: I just took another look. I thought parameters had to be annotated via block comments (that's how you have to do it if using CoffeeScript 2). I was wrong.

[0] http://www.lightscript.org/

The following example written in TS works in Flow too:

  type MyComponentProps = {
    prop1: string;
    prop2?: number;
  }

  type MyComponentState = {
    foo: number;
    bar: string;
    baz: number;
  }

  class MyComponent extends Component<MyComponentProps, MyComponentState> {

Same syntax.

Also, not sure how this could be more straightforward.

Thank you. I edited my comment after looking at the Flow website. My incorrect understanding came from seeing the atrocious "block comment Flow annotations" in CoffeeScript 2 (an otherwise adorable language) and thinking that was how you had to specify parameter types with Flow.