固定页脚与垂直滚动条重叠

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

window.addEventListener('scroll', function() {
  var footer = document.querySelector('.footer');
  var scrollHeight = document.documentElement.scrollHeight;
  var clientHeight = document.documentElement.clientHeight;
  var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
  
  if (scrollHeight - clientHeight <= scrollTop) {
    footer.style.position = 'static';
  } else {
    footer.style.position = 'fixed';
    footer.style.bottom = '0';
  }
});