proptype_array.js

import PropTypes from 'prop-types';

Widget.propTypes = {
  extraArray: PropTypes.array.isRequired,
  userNames: PropTyes.arrayOf(PropTypes.string).isRequired,
  userPosts: PropTypes.arrayOf(PropTypes.shape({
    id: PropTypes.number.isRequired,
    title: PropTypes.string.isRequired,
    body: PropTypes.string.isRequired,
    postDate: PropTypes.instanceOf(Date).isRequired
  })  
}