I had a modal with a simple form, with just an input field in it, and I wanted to put that element on focus as soon as the modal was added to the DOM by React.

I began thinking about many different ways to do so, maybe using useEffect() to trigger an event when the component was added to the DOM, or using the ref prop to create a reference to the DOM element and call its focus() method but then I realized I was thinking too complicated and just using the autofocus HTML attribute on the element could work.

And it did. Remember that it is autoFocus in JSX, with the capital F:

<input
  autoFocus
  ...// rest of the input field attributes