matchmediaReact.jsx

render() {
  const isSmallScreen = window.matchMedia('(max-width: 30em)').matches;
  
  return (
    isSmallScreen ?
      <p>This will only render if the window is smaller than 30em</p>
      :
      <p>This will only render if the window is 30em or more<p>
  );
}