class Demo extends React.Component {
    constructor(props) {super(props);}
    render() { console.log('rendering Demo'); return <h2>Testing</h2>; }}class Example extends React.Component{
   constructor(props){super(props); }
   componentDidMount(){
   setInterval(()=>{
         this.setState((state,props)=>({a:state.a+1}));
      },1000);
   }
   render(){
      console.log('rendering Example');
      return (<Demo y={1}/>);
    }}ReactDOM.render(
   <Example />,
   document.querySelector('div'));