set focus after submit react code example

Example 1: How to set focus on an input field after rendering?

componentDidMount(){
   this.nameInput.focus(); 
}

Example 2: react focus textarea

const focusDiv = useRef();

useEffect(() => {
 if(focusDiv.current) focusDiv.current.focus(); 
}, [focusDiv]);

return (
  <div ref={focusDiv}></div>
);