check if element is in viewport - vanilla JS. Use by adding a “scroll” event listener to the window and then calling isInViewport().

in_viewport.js

// Determine if an element is in the visible viewport
export default function isInViewport(element) {
  var rect = element.getBoundingClientRect();
  var html = document.documentElement;
  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (window.innerHeight || html.clientHeight) &&
    rect.right <= (window.innerWidth || html.clientWidth)
  );
}


// 
// Example on how you can use it.
//

import isInViewport from './functions/isInViewport';

window.onscroll = function() {
  let element = document.getElementById('your-id');
  
  if (isInViewport(element)) {
    // Do something
  }
}