CODE EXAMPLE FOR JAVASCRIPT

react-intersection-observer

import React from 'react';
import { useInView } from 'react-intersection-observer';

const Component = () => {
  //ref pass in element inView is true when we move to ref part in webpage
  const { ref, inView, entry } = useInView({
    /* Optional options */
    threshold: 0,
  });

  return (
    <div ref={ref}>
      <h2>{`Header inside viewport ${inView}.`}</h2>
    </div>
  );
};