class Demo extends React.Component {
constructor(props) {super(props);}
render() { console.log('rendering Demo'); return Testing
; }}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 ();
}}ReactDOM.render(
,
document.querySelector('div'));