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//fully

const isInViewport = (el) => {

  var rect = el.getBoundingClientRect();

  return {
    y: rect.top >= 0 && rect.bottom <= (window.innerHeight || document.documentElement.clientHeight),
    x: rect.left >= 0 && rect.right <= (window.innerWidth || document.documentElement.clientWidth)
  }

}


//partial

function elementInViewport2(el) {
  var top = el.offsetTop;
  var left = el.offsetLeft;
  var width = el.offsetWidth;
  var height = el.offsetHeight;

  while(el.offsetParent) {
    el = el.offsetParent;
    top += el.offsetTop;
    left += el.offsetLeft;
  }

  return (
    top < (window.pageYOffset + window.innerHeight) &&
    left < (window.pageXOffset + window.innerWidth) &&
    (top + height) > window.pageYOffset &&
    (left + width) > window.pageXOffset
  );
}