flow-no.js

class A extends Component {
  handleSomeEvent = (value: string) => {
    /* do stuff */
  }

  render() {
    return <B onSubmit={this.handleSomeEvent} />
  }
}

type Props = {
  onSubmit: Function
}

class B extends Component<Props> {
  handleSomeFormSubmitEvent: (event: Event) {
    this.props.onSubmit('some value')
  }
}