ReactJS: How to determine if the application is being viewed on mobile or desktop browser

Simple solution using react hooks

const [width, setWidth] = useState<number>(window.innerWidth);

function handleWindowSizeChange() {
    setWidth(window.innerWidth);
}
useEffect(() => {
    window.addEventListener('resize', handleWindowSizeChange);
    return () => {
        window.removeEventListener('resize', handleWindowSizeChange);
    }
}, []);

const isMobile = width <= 768;