Flow type function prop

index.js

// component
type AnotherType = {
  data: {
    id: string
  }
}

type Props = {
  aFunction: ({ id: string }) => AnotherType 
}

class Foo extends React.Component<Props> {
  doAThing = () => {
    // this does not trigger a flow error
    return this.props.aFunction('blahblah')
  }

  ...
}

aFunction: ({| id: string |}) => AnotherType