当div完全进入视区后，如何在页面底部粘贴div？

#stickyDiv {
  position: fixed;
  bottom: 0;
}

window.addEventListener('scroll', function() {
  var stickyDiv = document.getElementById('stickyDiv');
  var rect = stickyDiv.getBoundingClientRect();
  var windowHeight = window.innerHeight;

  if (rect.top >= 0 && rect.bottom <= windowHeight) {
    // div完全进入视区，将其添加到页面底部
    document.body.appendChild(stickyDiv);
  }
});