function Example(){
   const [a,setA] = React.useState(0);
   let i=0;
   React.useEffect(() => { console.log(2); return 0; });
   const m = React.useMemo(() => { console.log(0); return 0; },[])
   ;
   const n = React.useMemo(() => { console.log(1); return 0; });
   React.useEffect(() => { console.log(3); return 0; } ,[]);
   return (<button onClick={()=>setA(a+1)}>{a}</button>);}ReactDOM.render(<Example/>,document.querySelector("div"));