PropTypes to Flow blog post

proptypes-to-flow-example.js

/* 1) Using good old PropTypes */
function Button({ message }) => 
  <button>{message}</button>;
  
Button.propTypes = {
  message: PropTypes.oneOfType([
    PropTypes.string,
    PropTypes.number,
    PropTypes.instanceOf(Message)
  ]).isRequired,
};

/* 2) Using Flow annotations */
type Props = {
  message: string | number | Message,
};

function Button({ message } : Props) => 
  <button>{message}</button>;