Inne rozwiązanie.js

  var Component = createReactClass({
      render: function () {
          return React.DOM.span(null, "I'm so custom");
      }
  });

  ReactDOM.render(
      React.createElement(Component),
      document.getElementById("app")
  )

react create class without ES6.js

<script src="node_modules/create-react-class/create-react-class.js"></script>
<script>
  var MyComponent = createReactClass({
    render: function () {
        return React.DOM.span(null, "i'm so awesome")
    }
  });