function MyButton() {
   const [x,setX] = React.useState(0);
   const f = x=>{console.log('firing!'); return x;}
   const inputEl = React.useRef(f(null));   // f() called on every render even if ref not used
   return (<button onClick={()=>setX(x+1)}>Render</button>);}ReactDOM.render(<MyButton/>,document.querySelector("div"));