防止绝对位置。滚动时页脚div抖动

.footer {
  position: fixed;
  bottom: 0;
  width: 100%;
}

.footer {
  position: sticky;
  bottom: 0;
  width: 100%;
}

window.addEventListener('scroll', function() {
  var footer = document.querySelector('.footer');
  var footerHeight = footer.offsetHeight;
  var windowHeight = window.innerHeight;
  var scrollHeight = document.documentElement.scrollHeight;
  
  if (windowHeight + window.pageYOffset >= scrollHeight - footerHeight) {
    footer.style.position = 'fixed';
    footer.style.bottom = '0';
  } else {
    footer.style.position = 'static';
  }
});