function MyButton(props){     // return <button onClick={()=>props.onClick(count+1)}>+1</button>;  // error
     return <button onClick={()=>props.onClick(n=>(n+1))}>+1</button>;}function Example() {
   const [count, setCount] = React.useState(0);
   return (<div><p>Counter: {count}</p>
                      <MyButton onClick={setCount}/>
              </div>);}ReactDOM.render(<Example/>,document.querySelector("div"));