Custom hook for setting up an intersection observer on a DOM element to determine its visibility relative to a specified viewport or the default viewport. Implements the native `IntersectionObserver` JavaScript class.

useIntersectionObserver.js

/**
 * Custom hook for setting up an intersection observer on a DOM element to determine its visibility relative to a specified viewport or the default viewport. Implements the native `IntersectionObserver` JavaScript class.
 *
 * @param {React.RefObject} ref - Required. The React ref object pointing  
 * @param {Object} options - The options for setting up the observer.
to the DOM element to observe.
 * @param {Element|null} [options.root=null] - The element that is used as the viewport for checking visibility of the target. Defaults to the browser viewport if not specified.
 * @param {string} [options.rootMargin="0px"] - The margin around the viewport or "root". Can have values similar to the CSS margin property, e.g. "10px 20px 30px 40px" (top, right, bottom, left).
 * @param {number} [options.threshold=0.5] - A single number or array of numbers indicating at what percentage of the target's visibility the observer's callback should execute. Ranges from 0 to 1.
 * @returns {boolean} True if a current interection is present for the element for which the the React ref was pssed. False otherwise.
 * @example
 * function MyComponent() {
 *   const ref = useRef(null);
 *   const { isIntersecting } = useIntersectionObserver({ ref });
 *
 *   return <div ref={ref}>isIntersecting: { isIntersecting? 'Y' : 'N' }!</div>;
 * }
 *
 * @example https://codepen.io/HoraceShmorace/pen/GRLBBmM
 * @see Complete example at https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserver
*/

const useIntersectionObserver = (ref, options = {
  root: null,
  rootMargin: "0px",
  threshold: 0.5
}) => {
  if (!ref) throw "You must pass a reference {React.RefObject}.";

  const [entry, setEntry] = useState(false);

  const handleIntersection = (entries) => {
    const [entry = {}] = entries;
     setEntry(entry);
  };

  useEffect(() => {
    const rootElement = ref.current;
    const observer = new IntersectionObserver(handleIntersection, options);

    if (rootElement) {
      observer.observe(rootElement);
    }

    return () => {
      if (rootElement) observer.unobserve(rootElement);
      observer.disconnect();
    };
  }, [ref.current]);

  return entry;
};