<div id="content"></div>

var Counter = React.createClass({
  getInitialState : function() {
    return {
      count : 0,
      say : 'Hi'
    };
  },
  addCount : function() {
    this.setState({count : this.state.count+1});
  },
  render : function() {
    return ( 
      <div>
        count : <span>{this.state.count}</span><br/>
        say : <span>{this.state.say}</span><br/>
        <button onClick={this.addCount}>+1</button>
      </div>
    );
  }
})
ReactDOM.render( <Counter />, document.getElementById('content') );