shouldComponentUpdate(nextProps) {
        return this.props.children !== nextProps.children;
      }
      render() {
        return <span prop={this.props.children} />;
      }
    }
    class Content extends React.Component {
      shouldComponentUpdate(nextProps) {
        return this.props.step !== nextProps.step;
      }
      render() {
        return (
          <div>
            <Bar>{this.props.step === 0 ? 'Hi' : 'Hello'}</Bar>
            <Bar>{this.props.step === 0 ? this.props.text : 'World'}</Bar>
          </div>
        );
      }
    }
    function Foo(props) {
      return (
        <div hidden={true}>
          <Content step={props.step} text={props.text} />
        </div>