import PureRenderMixin from 'react-addons-pure-render-mixin'; const CharacterCounter = React.createClass({ propTypes: { text: React.PropTypes.string.isRequired, max: React.PropTypes.number.isRequired }, mixins: [PureRenderMixin], render () { const diff = this.props.max - this.props.text.length; return ( {diff} ); } }); export default CharacterCounter;