prop_types.js

import PropTypes from 'prop-types';

const ItemDiv = ({ name, price, purchaseHandler }) => {
  return(
    <div>
      div> Item:{name} </div>
      div> Price:${price} </div>
      <button onClick={purchaseHandler}> Purchase </button>
    </div>
  )
}

ItemDiv.propTypes = { 
  name: PropTypes.string.isRequired,
  price: PropTypes.number.isRequired,
  purchaseHandler: PropTypes.func.isRequired
}