function areEqual(prevProps, nextProps) {
   return (prevProps.y.a.b===nextProps.y.a.b);}const Demo = React.memo(props=>{
   console.log('rendering Demo');
   return <h2>{props.y.a.b}</h2>;},areEqual);class Example extends React.Component{
   constructor(props){
      super(props);
      this.state={a:{b:0}};
   }
   componentDidMount(){
      setInterval(()=>{
         this.setState((state,props)=>({a:{b:0}}));
       },1000);
    }
    render(){
       console.log('rendering Example');
       return (<Demo y={this.state}/>);
    }}ReactDOM.render(<Example />,
  document.querySelector('div'));