替代嵌套锚标签

a {
  text-decoration: none;
  color: blue;
}

a:hover {
  text-decoration: underline;
}

var links = document.getElementsByTagName('a');
for (var i = 0; i< links.length; i++) {
  links[i].addEventListener('mouseover', function() {
    this.style.textDecoration = 'underline';
  });
  links[i].addEventListener('mouseout', function() {
    this.style.textDecoration = 'none';
  });
}