Fixing Input Focus Issues with MUI Popper and React Refs

When using MUI’s Popper component in React, focusing an input element when the Popper opens can sometimes behave unexpectedly. I recently ran into this issue while trying to automatically focus an input field within a Popper.

Here’s a simplified version of the problem:

const Pagea = () => {
	const [open, setOpen] = useState(false);
	const ref = useRef();
 
	useEffect(() => {
		if (open) ref.current?.focus();
	}, [open]);
 
	return (
		<>
			<Button onClick={() => setOpen(prev => !prev)}>Click</Button>
			<Popper open={open}>
				<Paper>
					<input ref={ref} />
				</Paper>
			</Popper>
		</>
	);
};

The Problem

Despite setting the ref on the input and using useEffect to trigger focus, the input didn’t focus when the Popper opened. The ref seemed to be null when the Popper was first opened, even though the input existed in the DOM.

Why It Happens

This issue arises because Popper by default uses a react portal, rendering its children outside the React component tree. Since the input is temporarily moved out of the DOM hierarchy, React loses track of the ref during this transition, causing it to be null momentarily when the Popper opens.

The Fix

To solve this, simply add disablePortal to the Popper component. This prevents the Popper from being rendered in a portal, keeping the input within the normal React DOM tree and maintaining ref stability.

<Popper open={open} disablePortal>
	<Paper>
		<input ref={ref} />
	</Paper>
</Popper>

Now, when the Popper opens, the input will correctly receive focus.

Bonus: Fixing Position Issues

In certain layouts where parent elements have overflow-x or overflow-y set to hidden, you might notice the Popper covering its reference element. To ensure proper positioning, you can modify the Popper’s preventOverflow behavior:

modifiers: {
	preventOverflow: {    
		escapeWithReference: true  
	}
}

This helped the Popper avoid improper placement, ensuring it stays next to the element it’s supposed to align with.