example.js

var Form = React.createClass({
  focusOnField: function(){
      React.findDOMNode(this.refs.textField).focus();
  },
  render: function(){
      return (
          <div>
              <input 
                  type="text"
                  ref="textField" />
              <input 
                  type="submit"
                  value="Focus on the input!" 
                  onClick={this.focusOnField} />
          </div>
      );
  }
});
var App = React.createClass({
  render: function(){
      return (
          <div>
              <h1> Welcome to the focus app!</h1>
              <Form />
          </div>
      );
  }
});
React.render(<App />,  document.getElementById("app"));