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back to top summaryOct 08, 2016 pm 02:21 PM

回到顶部总结
网站中的回到顶部功能有益于增强用户体验,当一个页面很长很长时,回到顶部是必不可少的。
回到顶部按钮,可以使用图片,背景图,矢量字体图标,也可以使用代码 css 生成。这里使用 css 生成的方法。
html:<a href="" title="回到顶部" id="toTop">
   <span id="arrow"></span></a>

css:
#toTop {
   display: none;
   position: fixed; /* 固定定位 */
   right: 10px;
   bottom: 30px;
   background-color: #e6e6e6;
   height: 40px;
   line-height: 40px;
   width: 40px;
   transition: all .4s ease .1s;
}#toTop:hover { background-color: #b7b7b7; }#toTop span {
   position: relative; /* 相对定位,以便其伪元素绝对定位 */
   top: 5px;
   left: 15px; /* 变换为顺时针旋转 30°,通过数学角度计算后适当调整位置 */
   display: inline-block;
   width: 3px;
   height: 20px;
   background-color: #fff;
   border-radius: 3px;
   -webkit-transform: rotate(30deg);
       -ms-transform: rotate(30deg);
           transform: rotate(30deg);
}#toTop span:after {
   content: "";
   position: absolute; /* 伪元素中是相对于 #toTop span 绝对定位 */
   top: -5px;
   left: 8px;
   display: inline-block;
   width: 3px;
   height: 20px;
   background-color: #fff;
   border-radius: 3px;
   -webkit-transform: rotate(-60deg);
       -ms-transform: rotate(-60deg);
           transform: rotate(-60deg);
}

使用 css 代码生成的回到顶部按钮如下:

 
对于回到顶部的多种方法总结如下:
1. 锚标记
# 包含了一个位置信息,默认的锚是 #top 也就是网页的顶端。
方法:
1. 对回到顶部的按钮使用锚标记,即 a 标签,<a href="#top"  title="回到顶部">回到顶部</a>
2. 在页面的顶部放置定位目标,<a name="top" id="top"></a>,这里的 name 属性和 id 属性的值比第一步骤中的 href 属性的值少一个 #,name 和 id 选择一个即可。
缺点:
会在地址栏里多出 # 符号。
2. JavaScript Scroll 事件:
<a href="javascript:scroll(0, 0)" title="返回顶部">返回顶部</a>
scroll(0, 0) 中第一个参数是相对于屏幕的水平位置,第二个参数是相对于屏幕的垂直位置。可调整其中任意一个值。
3. animate 缓慢回到顶部:

js:
$(window).scroll(function () {    if($(window).scrollTop()>=100) {
       $("#toTop").fadeIn(400); /* 当滑动到不小于 100px 时,回到顶部图标显示 */
   }else {
       $("#toTop").fadeOut(400); /* 当滑动到小于(页面被卷去的高度) 100px 时,回到顶部图标隐藏 */
   }
});
$("#toTop").click(function () { 
   $("html, body").animate({scrollTop: 0}, 100); /* 持续时间为 100ms */    return false;
});


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