callbackRefFunction.js

const App = () => {
  const [value, setValue] = React.useState('highlight and copy me');
  let textInput;
  
  const handleClick = () => {
    textInput.select();
    document.execCommand('copy');
  }
  
  return (
    <div>
      <input type="text" ref={el => textInput = el} readOnly value={value}/>
      <button onClick={handleClick}>Copy</button>
    </div>
  );
};