foo.jsx

var counter = 0,
    repaint = () => React.render(document.body, <Spinner data={counter}/>),
    inc     = () => { counter += 1, repaint() },
    dec     = () => { counter -= 1, repaint() },

    Spinner = React.createClass({

        render: function() {

          return <div>
            {this.props.data}
            <button value="^" onclick={inc}/>
            <button value="v" onclick={dec}/>
          </div>;

        }

    });