返回顶部按钮能够帮助用户快速平滑的返回到页面的顶部。

HTML结构

在body标签结束之前添加返回顶部按钮：

<body>
  <!-- all your content here -->
 
  <a href="#0" class="cd-top">Top</a>
 
  <!-- link to scripts here -->
</body>

CSS样式

返回顶部按钮始终出现在页面的右边。初始化时它是不可见的：visibility:hidden; 和 opacity:0;。这两个属性可以通过2个class来控制：.cd-is-visible 和.cd-fade-out。

.cd-top.cd-is-visible {
  /* the button becomes visible */
  visibility: visible;
  opacity: 1;
}
.cd-top.cd-fade-out {
  /* if the user keeps scrolling down, the button is out of focus and becomes less visible */
  opacity: .5;
}

JAVASCRIPT

在demo中，我们使用三个变量来控制返回顶部按钮：

//browser window scroll (in pixels) after which the "back to top" link is shown
var offset = 300,
  //browser window scroll (in pixels) after which the "back to top" link opacity is reduced
  offset_opacity = 1200,
  //duration of the top scrolling animation (in ms)
  scroll_top_duration = 700;

offset变量用于切换.cd-is-visible类。offset_opacity用于控制.cd-fade-out。

返回顶部的动画使用的是jQuery .animate()方法。