gistfile1.txt

/** @jsx React.DOM */

var PanelGroup = ReactBootstrap.PanelGroup;
var Panel = ReactBootstrap.Panel;

var mountNode = document.body;
var renderedInstance;


var PanelGroups = React.createClass({
  render: function() {
    return (
      <PanelGroup activeKey={this.props.activeKey} onSelect={this.props.onSelect} isAccordion>
        <Panel header="Title 1" key={1}>
          <p>Content 1</p>
        </Panel>
        <Panel header="Title 2" key={2}>
          <p>Content 2</p>
        </Panel>
      </PanelGroup>
    );
  }
});


var Contract = React.createClass({
  getInitialState: function () {
    activeKey: 1
  },

  handleSelect: function (selectedKey) {
    this.setState({
      activeKey: selectedKey
    });
  },

  render: function() {
    return (
      <div>
        <p>Custom stuff</p>
        <PanelGroups activeKey={this.state.activeKey} onSelect={this.handleSelect} />
      </div>
    );
  }
});

renderedInstance = React.renderComponent(<Contract />, mountNode);

It worked with:

  getInitialState: function () {
    return {
      activeKey: 1
    }
  },

Thanks!