Edit in JSFiddle

const Star = ({ isActive }) => {
	const classNames = ['star'];
  const activeClass = 'star--active';
  
  if (isActive) {
  	classNames.push(activeClass);
  }
  
  return <span className={classNames.join(' ')}>★</span>;
};

const RatingWidget = ({ size, rating, onRatingChange, onChangeBegin, onChangeAbort }) => {
	var starItems = [];
  for (let i = 0; i < size; i++) {
    starItems.push(
      <li key={i} className="star-item" onClick={onRatingChange.bind(null, (i + 1))} onMouseEnter={onChangeBegin.bind(null, (i + 1))} onMouseLeave={onChangeAbort.bind(null)}>
      	<Star isActive={i < rating}/>
      </li>
    );
  }

	return (
  	<ul className="rating-widget">{starItems}</ul>
  );
};

const RatingWidgetContainer = React.createClass({
	getInitialState: function() {
  	return {
    	rating: this.props.rating
    };
  },
  
  handleChangeBegin: function(rating) {
  	this.setState({
	    rating: rating
    });
  },
  
  handleChangeAbort: function() {
  	this.setState({
	    rating: this.props.rating
    });
  },
  
  render: function() {
  	return <RatingWidget
              size={this.props.size}
              rating={this.state.rating}
              onRatingChange={this.props.onRatingChange}
              onChangeBegin={this.handleChangeBegin}
              onChangeAbort={this.handleChangeAbort}/>
  }
});

// model
let appState = {
	rating: 0
};

// controller
const updateRating = (newRating) => {
	appState.rating = newRating;
  renderApp();
};

// bootstrap
function renderApp() {
	ReactDOM.render(
    <RatingWidgetContainer size={5} rating={appState.rating} onRatingChange={updateRating}/>,
    document.getElementById('root')
  );
}

renderApp();

<div id="root"></div>

<script src="https://fb.me/react-0.14.8.js"></script>
<script src="https://fb.me/react-dom-0.14.8.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.34/browser.js"></script>

.star {
  color: #CCC;
  cursor: pointer;
}

.star--active {
  color: #FFDD99;
}

.star-item {
  display: inline;
}

.rating-widget {
  margin: 0;
  padding: 0;
  list-style-type: none;
}