在内外悬停时从左到右加下划线

Question

使用下面的代码，我得到一个从左到右的悬停下划线效果。

.underline {
  display: inline;
  position: relative;
  overflow: hidden;
}
.underline:after {
  content: "";
  position: absolute;
  z-index: -1;
  left: 0;
  right: 100%;
  bottom: -5px;
  background: #000;
  height: 4px;
  transition-property: left right;
  transition-duration: 0.3s;
  transition-timing-function: ease-out;
}
.underline:hover:after,
.underline:focus:after,
.underline:active:after {
  right: 0;
}

<p>hello, link is <a href="#" class="underline">underline</a>
</p>

当你不在悬停状态时，:after元素返回到左边的初始状态。是否有任何方法，:后去右，而不是左当你离开悬停?

Answer 1

你可以尝试用动画的宽度来代替右/左属性。

.underline {
  display: inline;
  position: relative;
  overflow: hidden;
}
.underline:after {
  content: "";
  position: absolute;
  z-index: -1;
  right: 0;
  width: 0;
  bottom: -5px;
  background: #000;
  height: 4px;
  transition-property: width;
  transition-duration: 0.3s;
  transition-timing-function: ease-out;
}
.underline:hover:after,
.underline:focus:after,
.underline:active:after {
  left: 0;
  right: auto;
  width: 100%;
}

<p>hello, link is <a href="#" class="underline">underline</a></p>

请看下面的示例:https://jsfiddle.net/1gyksyoa/

Answer 2

基于这个答案:扩展悬停的底部边框，你可以改变悬停的transform-origin属性来实现"hover out"你正在寻找的效果。下面是一个例子:

.expand{
  position:relative;
  text-decoration:none;
  display:inline-block;
}
.expand:after {
  display:block;
  content: '';
  border-bottom: solid 3px #000;  
  transform: scaleX(0);  
  transition: transform 250ms ease-in-out;
  transform-origin:100% 50%
}
.expand:hover:after { 
  transform: scaleX(1);
  transform-origin:0 50%;
}

Here is some dummy text <a href="#" class="expand">expand</a>